Cat That Ate The Canary Meaning

(idiomatic) A person whose appearance and behavior suggest guilt mixed with other qualities, such as satisfaction or feigned nonchalance.

Example: 1910, "Cotton Bulls Stand Shock of Deliveries," New York Times, 30 Apr., p. 2,
  He talked freely and carried the smile of the cat that swallowed the canary.
2001, "Joseph hints at hurt hand," (Canada), 25 Apr. (retrieved 9 Aug 2008),
  You have to hand it to Curtis Joseph. Not only does he keep pucks out of the net, he keeps secrets too. "It's taboo," said Joseph, grinning like the cat that ate the canary. "You're not going to get anything."
2007, Georgi Davis, "Jeans weather makes a woman do strange things," St Petersburg Times, 25 Feb. (retrieved 9 Aug 2008),
  I stood there looking like the cat that ate the canary. . . . But he knows me too well and pondered out loud what I had been up to.
2001, "Daytona 500: Andretti on Italian food, breakfast cereal and going fast," CNN/Sports Illustrated, 12 Feb. (retrieved 9 Aug 2008),
  Like the cat that swallowed the canary. Not only do you feel a little bit guilty 'cause you can't stop, but you feel pretty good, too.
2007, Lorena Mongelli and Eric Lenkowitz, "Idiot & Dummy: 'Car Fool' Cheater Nailed in HOV Lane," New York Post, 24 Feb. (retrieved 9 Aug 2008),
  Daley said that Tietjen, who lives in Middle Island, had the "cat who ate the canary" look when he was pulled over. The 32-year-old driver was apologetic, and never tried to dispute the ticket.