Are participants in stage hypnosis part of the show? Are the volunteers actually part of the performance (i.e. paid or in other ways compensated) to perform like chickens etc., or is it actually possible to hypnotize people in the short space of time that is given?

All hypnosis is a form of self hypnosis, and it is fairly well understood that you cannot hypnotize either:

* someone unwilling to be hypnotized
* someone to do something that they are utterly unwilling to do



Lots of studies cited, plus an interesting read nonetheless: CIA: Hypnosis in Interrogation

From my own experience being one of those fools willing to get on stage, the hypnotic suggestion just seems to be an "okay that sounds fun" as you're extremely relaxed and aware of the situation while not feeling so self-conscious. When the hypnotist suggested that we take our shirts off and turn them inside out (I being male) ... I snapped out as I'm very self-conscious of my body image and was excused from the stage.

I like the howstuffworks article on the subject and from my experiences it seems pretty spot on. You aren't so much asleep as you are hyper-aware of the suggestions of the hypnotist.