Researchers at the University of Sussex have discovered that cats use a "soliciting purr(ゴロゴロ喉を鳴らす)" to manipulate their owners into doing their bidding, especially when they want to be fed. Unlike regular, low frequency purring, this "solicitation purr" includes a higher-pitched sound with a frequency similar to a baby's cry, a sound humans are naturally inclined to respond to and find difficult to ignore.