Holes In Padlocks
If you keep a padlock outdoors, you should know that it would have broken down already if there was no hole at the bottom. The hole allows the water to go out when they do get in. Can you imagine how rusty they would otherwise get? In case it jams, you can just slip some oil or WD-40 in the same hole.
Detachable Car Headrests
It is practically a given that children seating in the backseat would mess around with the headrest in front of them. This is common during family road trips. The truth is that you can actually pull out the headrest all the way. They did this so that you can break the windows with the metal bars if you have to.