Turncat

Turncat (catfinition) – a cat who switches sides; a traitor.

In use:  “We would have struggled to find her,” authorities said, “except for a turncat who betrayed their owner to save Mr. Obama. The cat hair on the Obama package was microscopically consistent with the hair of one of Poff’s cats.”

“Would-be Obama assassin identified by cat hairs, authorities say”

h/t msn.com