I trained as a hypnotherapist many years ago (never actually practiced) and it is quite possible to just put your hand over someone's eyes and send them back into a trance! or tap a pencil on a table, or clap your hands, or touch them on the forehead, or pretty well anything. The first time I did it - in training - really shocked me as I had no belief that it would work.
You get someone suggestible, you hypnotise them a few times so they go into trance more and more easily, and then you plant some suggestions into their mind while they are under, along the lines of "I will whisper to you and you will fall instantly asleep, as deeply asleep as you are now", repeat a few times in slightly different words, bring them round, some time later you say the word or perform the action and bingo! That really is all you have to do.
FWIW, this whole thing would never get past an ethics committee anywhere except showbiz.
Let's pretend we think this poor lad Steve has been hypnotized, isn't an actor. He will have signed a waiver long before the potential candidates were whittled down to him. He's been through lots of personality profiling, psychological tests etc. to get the candidate who is most likely to come out unscathed. However, I'm still not comfortable about it.
Entertainment is getting more extreme. Ergo, DB is getting more extreme. I do admire DB's abilities, and I really like that he exposes 'psychic' ability as no such thing. In the early days, he was just amazing. Some of the things he does are great. I loved that he had bought that doll and restored it (on tv some time ago, I think it was one of his theatre shows, televised).
If he could hypnotize me and persuade my brain to mend my myelin sheaths I would worship him forever! I doubt even he could do that! Come on Derren Brown if you think you're hard enough! 