the revenge of the blonde

"A lawyer and a blonde are sitting side by side on an airplane during a long flight. The lawyer turns ... and asks if she wants to play a game to pass the time. The blonde is tired and refuses politely. The lawyer persists and says that the game is very simple and fun:
"I'll ask questions if you do not know the answer, u 'll give me some money and so will I if I do not answer your own question."
The blonde looks at him and repeats , that she is not interested. Lawyer makes another offer:
"Well, can i suggest something else? If you do not know the answer you will give me 5 euros and if i do not know I'll give you 500 euros. "
The blonde thinks again and finally agrees to play. The lawyer asks:
"What is the distance between the earth and the moon?".
The blonde looks at him without saying a word, opens her purse and gives him 5 euros. The lawyer smiles and takes the money. Now it's blonde's. so she asks him:
"What goes up the mountain with 3 legs and comes down with 4 legs?".
The lawyer looks at her puzzled. Turns out the laptop from the bag and looking for the answer , all over the net. Angry that does not find the answer sends e-mail to all his friends asking to get an answer. In vain , because no one knows. After an hour searching for the answer, opens his wallet and gives the blonde 500 euros. She takes it and goes to sleep . The lawyer clearly annoyed, pokes her and asks:
"Well, what goes up the mountain with 3 legs and comes down with 4 legs?".
The blonde and looks at him without saying a word, opens her purse , gives him 5 euros and goes back to sleep