Funny, but it could have caused serious injury.
In drivers ed classes, they call injuries caused by unsecured items flying from the back seat/rear window, etc., "the second collison". Unsecured items behind the driver/passenger area can become literal projectiles in a front-end collision.
I make a habit of not allowing unsecured stuff behind the driver/passenger area in my car. I try to put most things in the trunk, or secure them in the floor. I put the seat belts around larger items in the back seat.
It can save a life. Oh, this includes paint cans, too! LOL!