One day a frog comes about a black widow spider sitting on the bank of a river. "Hello Mr. Spider. How are you today?" says the frog. "Not too good,I'm afraid, Mr. Frog. I desperately need to cross the river but I'm not able to" says the spider. "Well I need to cross as well. If you promise not to bite me, I'd be happy to carry you across on my back" says the frog. "I promise not to, Mr. Frog! Thank you very much!" says the spider. The spider jumps onto the frog's back and they proceed to cross the river. Half way across, the spider bites the frog. As the frog slowly starts to sink into the river, he sadly asks "why did you do that, Mr. Spider? Now surely both of us will die." The spider then sadly replies "I'm sorry, Mr. Frog, but I couldn't help it. It's in my nature."