http://news.bbc.co.uk/2/hi/science/nature/8147566.stm Cats exploit humans with purring meows.
This is SO true. I was faced with evidence of it last night.
A stray kitty trotted up to me as I was getting out of my truck and followed me to my apartment door, doing that purrrooooar little sound and weaving through my legs. I gave in and fed it, figuring it was someone's cat that got loose. Right after it got the food, it hissed and growled and didn't want anything else to do with me.
The little sucker has learned begging well.