26 April 2016 Damaged snail shell
Mechanical damage usually occur when a snail falls or is dropped from height onto a solid surface. Such damage is usually not too dangerous and the animal is able to rebuild the lost part of the shell. If the damage is excessive, though, the snail will die.
The photo presents a snail with damaged shell in the front. Such damage is a result of the snail being clamped too hard with fingers or if the shell is still soft and fragile. The snail will still lay eggs as any other high quality reproducer, but would be rejected during a purchase, or treated as a second class specimen. Thus, extreme care must be taken and young and little snails should not be moved with fingers, let alone thrown around.