As we know that force is inversely proportional to area on which it is being applied.
now according to this law if the area increases the force decreases, when area decreases force increases.
now we know they on a nail bed there are about more than hundred nails. now due to increased no of nails area is also increased so the force decreases.
so the force applied on a person's body is very less than it looks. that's why a person can lie on a nails bed.

a person can lie on a bed of nails by increasing the area and reducing the pressure and we know this from the fact that pressure=force/area.therefore area in inversely proportional to the pressure applied and therefore by increasing the area pressure is reduced and a person can lie on a bed of nails without being harmed too much.
     i hope that this will help u plzzzzzzzzz....mark it as the brainiest .