Guy: “Doctor, my Girlfriend is pregnant but we always use protection and the rubber never broke. How is it possible?”
Doctor: “Let me tell you a story: There was once an old man going beaver hunting. When a beaver jumped infront of him, the old man grabs his cane by mistake, raises it anyway and says "bang" and beaver drops dead.”
Guy: “Nonsense! Someone else must have shot the beaver..”
Doctor: “Good! You understood the story. Next patient please.”
Some jokes I found