Einstein & a kid sitting next to each other on a flight

Einstein & a kid sitting next to each other on a Flight......

Einstein says:
"Let's play a game....
I will ask you a question,
if you don't know the answer, you pay me only $5???????? and if I don't know the answer, I will pay you $500????????????????????..."

Einstein asks the first question:
What's the distance from the Earth to the Moon...?
Kid: didn't say a word, instead reaches into his pocket, pulls out a $5 and gave it to him.

Now...
It's the kid's turn...

He asks Einstein:
What climbs up a hill on 3 legs and comes down on 4 legs..?

Einstein searches the net....; and asks all his smart friends...
After an hour he gives the kid 500$...

Einstein asks:
Well...so what goes up a hill with three legs and comes down with four..?

The kid reaches into his pocket and gives Einstein $5...

Einstein fainted.....

Moral:
You may be Einstein
But never underestimate kids ????