Why don't I have a tail?

I have mentioned before Sydney's love of animals, especially the four legged furry kind. She likes to pretend that she is a puppy and she crawls around on all fours, tongue out, barking at us and smiling. Today after playing puppy, she asked why she can't have a tail like Bebo, our dog. I tried to explain that little girls and boys don't need tails....well, that was not a satisfying answer for my little animal lover, she cried for quite some time wanting a puppy tail so she could wag it. Silly girl :)