cat that swallowed the canary, (look) like the

look like the cat that swallowed the canary

1. To appear smug and/or overly pleased with oneself to others, especially over something one has done, received, or accomplished. After her promotion, Janet spent the rest of the day looking like the cat that swallowed the canary.
2. To have the appearance of guilt but attempt to hide behind an air of smugness or feigned nonchalance. When questioned on the use of campaign funds for his own personal pleasure, the senator looked like the cat that swallowed the canary.
See also: canary, cat, like, look, swallow, that
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.

cat that swallowed the canary, (look) like the

Look both smug and guilty. The analogy dates back to the mid-nineteenth century and was used by many writers, especially mystery writers (Dashiel Hammett among them), in the first half of the twentieth century.
See also: cat, like, swallow, that
The Dictionary of Clichés by Christine Ammer Copyright © 2013 by Christine Ammer
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