An accountant gets one over on a lawyer

A lawyer and an accountant are sitting next to each other on a long flight from the US back to London. The lawyer leans over to the accountant and asks if he would like to play a fun game.

The  accountant just wants to take a nap, so he politely declines and rolls over to the window to take a few winks. The lawyer persists and explains that the game is really easy and a lot of fun. He explains "I ask you a question and if you don't know the answer you pay me £10".

Again the  accountant politely declines and tries to get some sleep. The lawyer, now somewhat agitated, says "OK, if you don't know the answer you pay me £10, and if you ask me a question and I don't know the answer I will pay you £100".

This catches the accountant's complete attention, and as he sees no end to this torment unless he plays,  he reluctantly agrees to the game.

The lawyer asks the first question. "What's the distance from the earth to the moon?" 
The  accountant doesn't say a word, reaches into his pocket and pays the lawyer £10.
The lawyer is disappointed but still encourages the  accountant to ask a question. He thinks for a moment and then asks the lawyer: "What goes up a hill with three legs and comes down with four?" Having asked the question he turns round and goes back to sleep.

The lawyer looks at him with a puzzled look. He takes out his laptop and searches all his references, he opens his laptop, logs on to the web and tries searching around wikipedia, tries google, yahoo and host of other serch engines but he gets nowhere. Frustrated he sends emails to all his collagues and friends. All at no avail.

After an hour he wakes the accountant and hands him £100. The  accountant  politely takes the £100 and turns away to get back to sleep. The lawyer, more than a little miffed, shakes the  accountant and asks, "Well, so what is the answer? What goes up a hill with three legs and comes down with four?"

Without a word the accountant reaches into his wallet, hands the lawyer £10 and goes back to sleep.