This morning I had a stroll in my neighborhood. I saw a dog pee and then I had 我的十万个为什么--动物篇..
Since there are many scientists and talented mothers in this community, I decided to post my questions here.

1. Why does a dog like to lift a rear leg when it pees ?
2. Why does a crane stand on one leg while it sleeps?
3. Why does a cat like to cover its shit with sand or earth? Hehe, this is a question ever since when I was a child.
4.  Why does a rooster sing in the early morning? I know that some time I sing in the bed in the morning when I am happy. Is a rooster happy? What about hen?