The Baird’s rat snake had internal parasites — specifically, Strongyloides. Treated with Flagyl and Panacur; will repeat Panacur in a couple of weeks. Fortunately not transmissable except via fecal contact so the rest of the collection ought to be fine. And once she’s clear of the little worms, she should start putting on some weight. She’s been eating well, but — as I guessed — the Strongyloides, which can inhabit the entire GI tract, were skimming the nutrition off the top. No wonder she’s so teensy.