Because the truck driver is walking!!
How can you drop a raw egg onto a concrete floor without cracking it?
If there are 6 apples and you take away 4, how many do you have?
Some months have 31 days, others have 30 days. How many have 28 days?
What goes up and down, but still remains in the same place?
What gets wetter and wetter the more it dries?
What has a head and a tail but no body?
How can you lift an Elephant with just one hand?
What is the sound of one hand clapping?