A cell's delicate membrane is all that protects its inner machinery. It must not rupture, or the living flesh will spill out into nothingness.

The creature from the abyss has no bones, only a gelatinous form contained by a tough, leathery membrane. You must not puncture it, for the flesh inside is a deadly acid.

The alchemist's homunculus grew inside a fluid-filled sac, a biological membrane of his own creation. The notes were emphatic: you must not expose the developing flesh to air before its time.