He isnt using stooges. It is possible.
In the beginning of the first clip he thanks the subject for participating. Essentially, he hypnotized the subject before. During that time he gave the subject something called a post hypnotic suggestion which usually consists of telling the subject that anytime after this moment that they here him say the word 'sleep' they will enter into this same deeply relaxed state. The arm pull is something called a shock induction where you get a subject to enter into a subconscious routine (handshaking). Once the subject is subconsciously following that routine, you shock the subconscious through the arm pull (called pattern interrupt). At this point, the subconscious mind is 'shocked' and looks for a way out. During this time, the verbal suggestion 'sleep' coupled with the post hypno suggestion moves the subject into a state of hypnosis.
In the second clip, the subject is already hypnotized. What the hypnotist does is something called fractionation. This means that the hypnotist repeatedly brings the subject out of trance and then puts them back into that state. Each time, the subject goes deeper into trance than before. During the second clip, the hypnotist uses a variety of induction techniques, including the rapid or shock inductions. Note that the hypnotist tells you that the second person is a somnambulist - meaning the subject is highly hypnotizable.
I am a clinical hypnotherapist who mostly works with trauma. I use shock inductions as well as more traditional hypnotic scripts. I remember the first time I learned and practiced rapid inductions, I thought to myself "aint no way this is going to work". After trying it out on my classmate, who dropped deeply into hypnosis, I was a little shocked myself.
If you are interested in this stuff, I would suggest getting the book "Trancework" by Yapko. If you like the rapid inductions, take a look at Tom Silvers "Ultimate Shock Inductions" 2-DVD set. Richard Nongard also has a few vids that are fairly straightforward.
Also google the words I've italicized. You can find out more there.
