Do animals have a sense of humour?

Notice how your cat hides behind the curtain and jumps out at you, when you at your most relaxed, only to scare you out of your skin! Afterwards, she will prance around the room with her tail held high and this scheming glint in her eye. When she purposely wakes you an hour earlier on weekends for no particular reason as her food bowl is full, and just trots contentedly away as you scowl at her back you know she is giggling at your disgruntled glare. Dogs will fetch the stick you through them only to refuse to give it up, all the while watching you struggle and attempt to retrieve the stick to no avail. As soon as you give up, he will drop it at your feet and give you an oh so innocent look. Thus it is obvious that your pets have a sense of humour, whether it be sadistic of teasing, they amuse themselves often at our expense.