Cats have a specific “manipulative” purr.

Mommy’s Snugglebum, originally uploaded by bubblecup.etsy.com.

I see what yer doin’ there!

From the “I already knew this, but someone did formal research on it” department: Research indicates cats have a “manipulative” purr which differs from normal/pleasure purring. The manipulative purr is specifically used to get food and attention.  No shit,  really?