Big Balls

We see alot of trucks with the bull balls hanging from the trailer hitch or rear bumper.  All colors:  red, white, blue, yellow, green.  I saw a multi-colored pair on a big four-wheel drive pickup.  Hilarious to see a woman driving a truck with pink bull balls.  The ones that we see appear to be rubber or hard plastic and sway around while the truck is travelling down the highway.  We saw this truck on Monday morning.  The bull balls were huge and must be made out of aluminum or something metal.  They must be really heavy because they didn't move around at all and had a huge hole through the sides, apparently to reduce the weight.  Cracked us up.