Q: What did the dog say when he rubbed sandpaper on his tail?
A: Rough, rough!
Explanation: Another wonderful, classic dog joke! Sandpaper is rough, it is used to make things smooth. In English, when a dog barks it says, “Ruff.” This joke is funny because it plays with two words that sound the same, ruff and rough.
Rough, by the way, can also mean difficult: I had a rough day.