Grandpa was driving with granddaughter

Grandpa was driving together with his 9 yr outdated granddaughter and beeped the horn by mistake.

She turned and checked out him for an evidence.

He mentioned, “I did that accidentally.”

She replied, “I do know that, Grandpa.”

He replied, “How do you know?”

She mentioned, “Since you didn’t say, ‘Fool!’ afterward.”