Tinribs
"Some time in the fifties car makers discovered that if the bonnet opens while you are mobile bad things can happen.
They decided to have two latches one holds the bonnet closed good and proper the other just holds it more or less down but stops it coming any further up. It also allows it to project a bit so you notice the upsticking and vibrate a bit so you wonder what the noise is
They did this because they knew every so ofter one latch just isn't enough"
We call this method of working a FAIL SAFE do we not?