A hyena can only go to one watering hole as it's the only one for miles around. To get there he has to go through a clearing but every time he does a lion jumps out and beats him up.
This happens day after day and he's getting sick of it.
One day he staggers down to the watering hole after a particularly savage beating and gets talking to his mate the rhino.
He asks the rhino if he'll go with him the next day to protect him from the lion "of course" says the rhino.
So, the next day they set off together, hyena in front, rhino behind and sure enough on reaching the clearing out pops the lion and starts beating up the hyena.
The rhino just stands and watches.
10 minutes later the lion runs off and the hyena, lying bruised and battered askes him why he didn't intervene.
"Weeeelll" says the rhino, " you were laughing so much I thought you were enjoying it!"