What part of psychology is this?

I was just talking to my 2 friends for about an hour and I was completely messing with their brains. They wanted to know the name of someone and what I would do is give them a hint and then detour them and put them off track initially setting them back to where they started. I would say the persons name in context without them realizing it and 20mins later I'd say "I just said her name". I wanted to know what this would be classified as? I was completely confusing them and at the end they both said that they feel "mentally exhausted" and I really thought it was funny :) I've done this before but I think if I read up on it I'd be better at it.