Little Johnny walks in on his mother in the bathtub. He asks his mother what is the big fuzzy patch below her bellybutton. She replies, "A bush."
The next day Little Johnny walks in on his father while he's in the shower. He asks, "What is that big long thing hanging between your legs?" His father replies, "It is a snake."
A few days later, Little Johnny walks in on his mother, once again in the bathtub. He asks, "What are those two baggy things hanging above your bellybutton?" She replies, "Headlights."
A couple weeks go by and the little boy walks in on his parents having sex. He yells, "Mom, turn on your headlights! The snake is crawling into your bush!"