One day, little Bobby’s parents decided to have sex

So to get him out of the house they tell him to go to the balcony and count the number of red cars on the road, Bobby says sure and goes out.

After they've finished having sex they call him inside and ask him " So how many red cars did you see?", Bobby says " I didn't see any red cars but I found out our neighbours Mr and Mrs Smith were fucking" his dad laughs and says "That’s funny, did they leave the curtains open?”

In return, Bobby says out loud, "No I saw their son on the balcony counting red cars"