My personal favorite is when people say "That's creepy" (in the astonished kind of way, not the scared kind of way). It's my favorite because I didn't just amaze them; I truly got into their head and shook them to their core. I usually get this reaction with mental magic/mentalism effects. It doesn't really happen with very visual effects. It happens most when the spectator and their perceptions are involved, for example mind reading effects or PK touches. Now, I want to hear what your favorite reaction is, and why it's your favorite.