Here is a brain teaser below that I hope you haven't heard already. Try not to read other people's post before you answer.
A son and his father were in a car when the engine died in the middle of the railway cross. Despretly, the father tried to start the engine again as the oncoming train beared down on them to no avail. The father was killed and the son was sent to the hospital.
At the hospital, the surgeon was expecting a normal routine, but on seeing the boy, the surgeon goes pales and mutters: "I can't operate on him. He's my son."
How could that be??
I will give rep to the first few people with the right answer and also people who has an interesting answer too