From Derren Brown's Tricks of the Mind:

I always used to finish with the invisibility suggestion, but as I would generally follow the performances with an informal chat about it all, I would always ask the subjects what they had actually experienced.

Out of the, say, ten or so subjects who were given the suggestion, the responses might break down in the following way. Two had obviously been able to see me and had been openly separated from the rest of the group. Two or three would swear that the puppet and chair were moving all on their own and they could not see me, even though they may have guess I was somehow remotely responsible for the chaos that ensued. The remaining five or six would generally say they were aware I was there moving the objects, but that something in them would keep trying to blank me out, and they could only act as if I were invisible.