When a house cat wants something such as food or a trip outside, it sometimes adds a slightly irritating or annoying sound to its normal purr. The sound is adjusted to be just enough annoying to get what it wants from its owner. When it makes this kind of purr sound, the cat gets what it wants without making its owner angry! This is communication—or is it manipulation?!?—at its best!
Source: Cell Press (2009, July 13). House Cats Know What They Want And How To Get It From You. ScienceDaily. Retrieved July 14, 2009, from http://www.sciencedaily.com/releases/2009/07/090713121348.htm