A bunch of cows and bulls

A bunch of cows and bulls are standing in a field. A huge gust of wind comes along and all the cows fall over, but the bulls just stand there, bracing themselves against the gale.

All the cows stand up and go back to their chewing.

Pretty soon, an even stronger wind blows through and all of the cows are knocked to the ground, but the bulls just munch on the grass.

Next, a bona fide tornado comes through and all the cows are knocked clean into the next pasture. The bulls just say, "Mooo..."

Finally, one of the cows walks up to one of the bulls and says, "Moo? Is that all you can say? How come the wind always knocks us right over and you just stand there?"

"Isn't it obvious?" the bull replies. "We bulls wobble, but we don't fall down."