Grrrrrrrrrrrrrrrr........

Here's the questions:

There are 7 girls in a bus.
Each girl has 7 backpacks.
In each backpack, there are 7 big cats.
For every big cat, there are 7 little cats.

Question: How many legs are there in the bus?
Ok, the answer is NOT "none, because buses don't have legs!" Rather obviously referring to the catbus from Studio Ghibli, I guess. Click on the bus for the original puzzle. (I figured it out, by the way.)