I saw a post on Reddit shortly after the episode aired that had some nice speculation about the Moopsy's biology. It speculated that the Moopsy has a hydrofluoric-acid-based biology, with tissues based on fluorocarbon polymers, ie, squeaky plastic akin to teflon. Hydrofluoric acid is intensely toxic and dangerous to Terrestrial biology in a lot of ways, but if you spill hydrofluoric acid on yourself one of the things it does is seep straight through into your bones and start dissolving them. It really likes calcium, apparently.
According to this safety manual:
HF readily penetrates human skin, allowing it to destroy soft tissues underneath and to decalcify bone (hypocalcemea).
And down in the treatment section on this page:
Calcium gluconate (a calcium sugar) containing gels, solutions, and medications are used to treat hydrogen fluoride poisoning.