Thawed

A man found a huge block of ice. Frozen inside that block of ice was an adorable little pussycat. The man thought to himself: "I must rescue that pussy cat and bring it back to life." Swiftly, the man thawed the block of ice. When the block of ice finally melted, the pussy cat was freed -- but, suddenly, the cat turned into a mouse.

At which point, the man exclaimed to himself: "Oh, I thought I thawed a putthycat!"