Speed

A family of tortoises went into a cafe for some ice cream. 

They sat down and were about to start when father tortoise said, "I think its going to rain, Junior, will you pop home and fetch my umbrella?"

So off went Junior for father's umbrella, but three hours later he still hadn't returned.

"I think dear," said mother tortoise to father tortoise," that we had better eat Junior’s ice cream before it melts."

And then a voice from the door said, "If you do that I won't go."