It's the folk-rock polka music that really makes it.
What's most impressive about this illusion is how it manages to trick your brain, even after you've worked out the whole split-body, black-and-white outfit situation that makes it work. Try as you might, and conscious of the gimmick though you may be, it's more or less impossible to watch without lapsing back into the illusion.
Plus, like we said, there's the folk-rock polka music. Which adds a whole extra layer to the hypnotic nature of the experience.