system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do cast saws not cut the skin, but effectively cut the cast off of a limb?
gpt
Skin is wiggly.  You can wiggle it back and forth endlessly without damagine it as long as you only wiggle it a small distance.  The saw teeth on a cast cutter move a very small distance, about three thumbnail-thicknesses.  Over this short distance skin wiggles with no damage.  Plaster, on the other hand, is the opposite of wiggly.  Any tiny movement of a piece of plaster relative to the central mass breaks the piece off.  The cast cutter breaks off tiny dust-like bits of plaster as it cuts, merely wiggling the skin underneath.