Did you know", Matilda said suddenly, "that the heart of a mouse beats at the rate of six hundred and fifty times a second?"
I did not," Miss Honey said smiling. "How absolutely fascinating. Where did you read that?"
In a book from the library," Matilda said. "And that means it goes so fast that you can't even hear the separate beats. It must sound like a buzz."
It must," Miss Honey said.

Roald Dahl