Decibel's joke

This morning I come outside, lagging behind, but not last, that was Ralph, so I figured I was doing well.  Harold is sitting on the steps, chatting animated with someone, and giggling.  Decibel is giving him a smooch.

"What's so funny?"  I ask, trying to figure out which shoe goes where.
"Decibel told me a joke," Harold claims.

"What's big and brown?"

                                               "---    ME!"

Then he was laughing again, with Decibel hugging him, wagging her tail like mad and licking his face.  She is a very enthusiastic kisser.  Apparently she also tells jokes now.