Usually sometimes if you trip on something hard, If it get's stuck or slammed, Umm what else? Oh! If you pick on it, Or bite it. Thats usually all.
Too small shoes.
Trauma to the toenail can cause it to die off. An infection within the nail can also cause it to die off.
fungi and dirt
It's not.
Obviously you can break your ankles if you go on to pointe too early :P You can get blisters, bunions, your toes can break, you could rip a muscle. Their are many, many different injuries , some mor common then others :) You can also get bunionettes, plantar fasciitis, HUGE blisters, ingrown toenails, ripped-off toenails, and pretty much any horrific thing you can think of to happen to toenails.
Well, if your cockatiel's toenails are falling off, it probably has some kind of sickness. take him/her to the vet and see what he says.
You need to visit a physician to have lines on your toenails checked. This could be a sign of serious conditions that only a doctor can diagnose.
the car will break or shut off automaticly
Your toenails fall off
Yes, if you trim them off your toe first.
Yes it is normal
It means... you are going insane.