Little Johnny is walking along with his father and they pass two dogs that are going at it. He says, "Hey, Pop! What's happenin' over there?"
His father says, "Er... son, they're making a puppy."
That night, Little Johnny walks past his parents bedroom, and the old man's giving it to the old lady. Little Johnny says, "Hey, Pop! What's happenin' now?"
His father says, "Er...son, we're making you a baby brother."
Little Johnny says, "Well, flip her over. I'd rather have a puppy."