Fringe/Recap/S01 E09

Season 1, Episode 9:

The Dreamscape
A Massive Dynamics employee leaps out a window to his death after imagining that thousands of butterflies are cutting him and having the cuts actually appear on his body. John Scott appears to Olivia again, prompting her to go back in the sensory depravation tank to try and access more of John's memories. It leads them to an associate of John's, who confesses to dosing people with a toxin but claims that Massive Dynamics is the real culprit behind the Pattern. This confirms Olivia's suspicions, but before the suspect can say any more, he is dosed with the toxin and imagines his throat being slit.