My cat purrs very loud when he thinks he's getting away with a crime
Because he has a habit of biting my toes (only my toes, by the way, my wife gets to have her toes, only I am not allowed to have toes), I don't let my cat in the bedroom when I'm going to bed.
Naturally, this means he very much wants to be in the bedroom.
Now, for a tiny 8-pound cat, he has a hell of a motor, and on top of that, I have 100+ year-old hardwood floors from trees denser than what's around today. Stuff's basically concrete at this point.
Every once in a while, I will scan the room, not see the cat, and close the door. If he is hiding somewhere in the room, he will at this point start purring extremely loudly completely giving away whatever he's hidden under/behind. The floors amplify it, but I think it's funny if he forever thinks we can't hear purring, so I always let him get away with it (until he bites my toes five minutes later).