Ask the Tick: How many legs?

There are 7 girls in a vanpool. Each girl has 7 backpacks. In each backpack, there are 7 big cats. For every big cat, there are 7 little cats. How many legs are there in the bus?

The Tick answers, courtesy of Cha Cha*

Editor's note: I love questions that feature little cats with their little legs. 10,976 little paws!

*And Bonsai, and Larry who already posted the answer