6x19 (Spellbound) Greg mentions his grandmother being "psychic" and running fortune telling out of her kitchen. His family seemed to think he had the gift as well, though it's more or less "debunked" by him failing to figure out what Grissom was thinking. Whether or not it was just Greg trying to be funny or not remained to be seen.
The Wikipedia article on Greg claims "This is humorously referenced on several occasions, with Greg making a seemingly innocuous comment, which later either occurs or is referenced. Ironically, Greg is never present when these discoveries are made, and nobody ever seems to notice as well." (Greg Sanders "Family" entry)
Season 13 spoilers start here
However in 13x21 (Ghosts of the Past), the team winds up investigating a murder in an abandoned meat factory where a group of self proclaimed "ghost hunters" had gone to try and rouse the ghost of a serial killer 20 years dead. One of their own was brutally murdered in a frightening similiar fashion to the original killings, and up until the reveal of the flesh and blood killer, the lines of "spirit world versus real world" seemed to be actively toyed with, especially regarding Greg and his possibly "latent" powers.
Among the ghosts hunters, a young girl named Carrie Sinclair claimed in their initial encounter that she could "feel the presence of the [victims of Simms]" in the factory. He talks to her about ghost hunting, how long she's done it, and she admits that she's always felt the presence of the "other side" though ghost hunting is a recent endeavor for her. He takes notice of a pendant with four names (possibly angelic names but one is misspelled) around her neck, to which she claims it's always protected her at times of nee.
At first Greg seems uncertain, even outright skeptical about Carrie's claim, but in a moment with Morgan Brody later during the investigation, he turns around after finding a "shrine" dedicated to the victims from 20 years prior, looking as though he heard something but claiming it was "nothing" when Morgan asked what was wrong.
Later, when her partner, surviving male of the ghost hunters had been accused of murder and brought in for questioning, Carrie approached Greg to lay claim to her partner's innocence in the event. Carrie realizes through Greg's statement that evidence says otherwise, he had gone in to the slaughterhouse. Easily dismissible as common information given that he's a CSI and it is his job.
However the conversation following her statement is where it gets... interesting, coming from a woman who had, up until a few days prior, had never even spoken to Greg.
Carrie: You went in to the slaughter house, didn't you?
*Greg gives a frustrated sigh, but no answer*
Carrie: You know now what I was talking about. Those little boys--...
Greg: The only thing I felt in there, was cold. If you'll excuse me.
*Greg moves around Carrie to leave. Carrie turns around.*
Carrie: Why are you denying your gift?
*Greg slows and stops, looking uncertain*
Carrie: Your grandmother is still with you, you know. Even if you try to push her away she's still there.
*Greg turns around slowly, looks around uncomfortably, and then returns to Carrie speaking quietly.
Greg: What do you know about my grandmother?
Carrie: She had a funny name. ... *small laugh* Olaf, was it? She was a psychic, seems to think you are, too.
*At this point Greg looks torn between wanting to believe her, and still doubting.*
Carrie: You share her gift.
Greg: *Irritated, after a pause* What do you want from me.
Carrie: *Tearful* Your help. I heard those boys. I know they were tyring to say something I-I just don't know what it is.
Greg: *attempting to sound unconvinced, but some emotion slips through* I'm sorry, but I can't help you.
*Carrie removes the pendant from around her neck, at which point Greg scoffs.*
Greg: Thanks but... I don't want that.
*Carrie forcibly takes his hand and places it in his palm*
Carrie: You need it.
*Carrie then walks off, leaving Greg with the pendant*
Later, while Hodges and Henry, two lab techs are attempting to prove or disprove the other hunter's innocence back in the slaughter house, Carrie turns up dead, beaten to death by a metal baseball bat. When Greg and Morgan come to investigate her untimely death, he finds her EMP recorder that caught her voice at the time of death, trying to speak once more to the boys in the shrine area. When silence falls over after her voice, Greg finds himself listening closely as if he can possibly hear something, at which point Morgan finally confronts him about it and he admits "I used to be kinda psychic," and that when the time came in his life to choose science or "the other", he chose science. Morgan tries to argue that there's nothing there, that the supposed scientific cause of "haunting" had been something called "Infrasound", a low frequency pitched caused by large fans deeper in the building. She claimed she didn't feel anything since they had been turned off by Hodges and Henry.
Greg claimed he still did.
Whatever's going on, real life killer or not, Carrie's death gets to him in a personal way, and when he finds out that the place is about to be demolished since the crime scenes had been released, he forced himself out there alone. But only after Morgan confronted him, both of them agreeing that his ideas of "maybe hearing something from Carrie or the boys" was crazy but that he couldn't just leave well enough alone.
Only to find himself in the building alone with the actual real killer, a victim of Simms 20 years previous that had been used as bait for the other boys. No ghostly signs, no voices, nothing. Just enough silence for him to hear the ring tone that had been caught on Carrie's EMP recorder.
It's never explained, how Carrie knew about Olaf or Greg's gift. Greg even admits to Morgan he's not so sure anymore, what was reality and what was him just hoping for something supernatural to give clout to Carrie and his earlier feelings.
But when he puts the pendant on a hook in his locker and closes it to leave and go to breakfast with Morgan, the locker door swings open on it's own volition...
In a world were science likes to debunk the "super natural" from everything to vampires and werewolves and aliens, it does seem odd that something like ghosts and sixth senses would be toyed with so much more tongue and cheek, while also throwing back to statements already made by Greg in far earlier seasons. And even played with, humorously, with the idea that he can sometimes say something only for it to come true when he can't be there to witnesses it.
That said... who knows. Morgan made a good point in the ending, that in our world of science it's entirely possible there's far more unknown than known in the world and the universe. Greg is a good CSI, an intelligent person all around...
Maybe he does have a little bit of "the gift" that Carrie was so insistent he was ignoring?
The Wikipedia article on Greg claims "This is humorously referenced on several occasions, with Greg making a seemingly innocuous comment, which later either occurs or is referenced. Ironically, Greg is never present when these discoveries are made, and nobody ever seems to notice as well." (Greg Sanders "Family" entry)
Season 13 spoilers start here
However in 13x21 (Ghosts of the Past), the team winds up investigating a murder in an abandoned meat factory where a group of self proclaimed "ghost hunters" had gone to try and rouse the ghost of a serial killer 20 years dead. One of their own was brutally murdered in a frightening similiar fashion to the original killings, and up until the reveal of the flesh and blood killer, the lines of "spirit world versus real world" seemed to be actively toyed with, especially regarding Greg and his possibly "latent" powers.
Among the ghosts hunters, a young girl named Carrie Sinclair claimed in their initial encounter that she could "feel the presence of the [victims of Simms]" in the factory. He talks to her about ghost hunting, how long she's done it, and she admits that she's always felt the presence of the "other side" though ghost hunting is a recent endeavor for her. He takes notice of a pendant with four names (possibly angelic names but one is misspelled) around her neck, to which she claims it's always protected her at times of nee.
At first Greg seems uncertain, even outright skeptical about Carrie's claim, but in a moment with Morgan Brody later during the investigation, he turns around after finding a "shrine" dedicated to the victims from 20 years prior, looking as though he heard something but claiming it was "nothing" when Morgan asked what was wrong.
Later, when her partner, surviving male of the ghost hunters had been accused of murder and brought in for questioning, Carrie approached Greg to lay claim to her partner's innocence in the event. Carrie realizes through Greg's statement that evidence says otherwise, he had gone in to the slaughterhouse. Easily dismissible as common information given that he's a CSI and it is his job.
However the conversation following her statement is where it gets... interesting, coming from a woman who had, up until a few days prior, had never even spoken to Greg.
Carrie: You went in to the slaughter house, didn't you?
*Greg gives a frustrated sigh, but no answer*
Carrie: You know now what I was talking about. Those little boys--...
Greg: The only thing I felt in there, was cold. If you'll excuse me.
*Greg moves around Carrie to leave. Carrie turns around.*
Carrie: Why are you denying your gift?
*Greg slows and stops, looking uncertain*
Carrie: Your grandmother is still with you, you know. Even if you try to push her away she's still there.
*Greg turns around slowly, looks around uncomfortably, and then returns to Carrie speaking quietly.
Greg: What do you know about my grandmother?
Carrie: She had a funny name. ... *small laugh* Olaf, was it? She was a psychic, seems to think you are, too.
*At this point Greg looks torn between wanting to believe her, and still doubting.*
Carrie: You share her gift.
Greg: *Irritated, after a pause* What do you want from me.
Carrie: *Tearful* Your help. I heard those boys. I know they were tyring to say something I-I just don't know what it is.
Greg: *attempting to sound unconvinced, but some emotion slips through* I'm sorry, but I can't help you.
*Carrie removes the pendant from around her neck, at which point Greg scoffs.*
Greg: Thanks but... I don't want that.
*Carrie forcibly takes his hand and places it in his palm*
Carrie: You need it.
*Carrie then walks off, leaving Greg with the pendant*
Later, while Hodges and Henry, two lab techs are attempting to prove or disprove the other hunter's innocence back in the slaughter house, Carrie turns up dead, beaten to death by a metal baseball bat. When Greg and Morgan come to investigate her untimely death, he finds her EMP recorder that caught her voice at the time of death, trying to speak once more to the boys in the shrine area. When silence falls over after her voice, Greg finds himself listening closely as if he can possibly hear something, at which point Morgan finally confronts him about it and he admits "I used to be kinda psychic," and that when the time came in his life to choose science or "the other", he chose science. Morgan tries to argue that there's nothing there, that the supposed scientific cause of "haunting" had been something called "Infrasound", a low frequency pitched caused by large fans deeper in the building. She claimed she didn't feel anything since they had been turned off by Hodges and Henry.
Greg claimed he still did.
Whatever's going on, real life killer or not, Carrie's death gets to him in a personal way, and when he finds out that the place is about to be demolished since the crime scenes had been released, he forced himself out there alone. But only after Morgan confronted him, both of them agreeing that his ideas of "maybe hearing something from Carrie or the boys" was crazy but that he couldn't just leave well enough alone.
Only to find himself in the building alone with the actual real killer, a victim of Simms 20 years previous that had been used as bait for the other boys. No ghostly signs, no voices, nothing. Just enough silence for him to hear the ring tone that had been caught on Carrie's EMP recorder.
It's never explained, how Carrie knew about Olaf or Greg's gift. Greg even admits to Morgan he's not so sure anymore, what was reality and what was him just hoping for something supernatural to give clout to Carrie and his earlier feelings.
But when he puts the pendant on a hook in his locker and closes it to leave and go to breakfast with Morgan, the locker door swings open on it's own volition...
In a world were science likes to debunk the "super natural" from everything to vampires and werewolves and aliens, it does seem odd that something like ghosts and sixth senses would be toyed with so much more tongue and cheek, while also throwing back to statements already made by Greg in far earlier seasons. And even played with, humorously, with the idea that he can sometimes say something only for it to come true when he can't be there to witnesses it.
That said... who knows. Morgan made a good point in the ending, that in our world of science it's entirely possible there's far more unknown than known in the world and the universe. Greg is a good CSI, an intelligent person all around...
Maybe he does have a little bit of "the gift" that Carrie was so insistent he was ignoring?