Be afraid.

According to this article from the BBC, cats manipulate their human owners into providing food and attention by shifting the pitch and tone of their purrs. The wily little bastards aurally mime the cry of infants, flicking on whatever primordial ma/paternal protect-the-kids switch is programmed into our brains. So when Beaker, my neurotic, corpulent little tuxedo cat wakes me up at four in the morning to get fed, it's that nutso purr that stops me from ignoring it.

Insidious.