The ancients knew about mannequins, I'm sure of it.
In the ancient language of magic, this section of the book says "Modern Spells." Let me see if I can translate this random spell.
Smooth rigid skin? The description sounds like it is describing the skin turing into a plastic shell, "no longer flesh so fair." There's also the implication that the body hollows out.
Hmm, this says to say how long but make it fit the verse.
Okay. Here goes.
A plastic shell, once flesh so fair,
Hollow now, long as I would dare
Three days will I be locked within
Nothing more than a mannequin.
Oh, it's working. Cool.