I'll confess I have tried this once or twice and never got it to work. However, if you want the proof, just have a search on Youtube!!
I've read that it's some sort of inbuilt response to a predator attack that makes them just stay still and 'play dead' rather than actual hypnosis, but it could actually be quite traumatic for the chooks I suppose (which is why I didn't persevere with hypnotising mine!!).