The engineer builds a square fence around the sheep and says "That's the best I can do".
The physicist wraps a fence around the equator and slowly shrinks it until it encounters the first sheep, then says "That's the best I can do".
The mathematician smirks and takes a meter-long length of fence, wraps it around himself and declares triumphantly "I define myself to be outside!"
--
John and Michael are in a floating balloon above a canyon.
John turns to Michael and says "I think we're lost", so Michael leans over the canyon and shouts "CAN ANYONE HELP US? WE DON'T KNOW WHERE WE ARE!"
His shout echoes in the canyon and a few minutes later they hear "YOU'RE IN A FLOATING BALLOON ABOVE A CANYON!"
John laughs and says "That's must've been a mathematician."
"How do you know?" asked Michael.
"Simple, his answer was completely accurate and utterly useless".
I know about a billion more but that's enough for now.
