Frog Skin: organ and chemical weapon
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In the middle of the season, a character notes that they’ve been running into frogs of a respectable size and calls them unappetizing creatures on account of how slimy they are. The remark is played for laughs, but it rests on a real biological fact: amphibian skin mucus is quite real, quite palpable, and serves a specific purpose that the series only brushes past.
The subject in depth
Amphibian skin is thin, permeable, and has no scales or hair. This lack of a physical barrier is compensated for by two types of dermal glands [Wikipedia] .
The mucous glands continuously produce a watery film. This mucus serves several roles: it keeps the skin moist, essential for cutaneous respiration (frogs absorb part of their oxygen directly through the skin), and it forms a slippery surface that makes a predator’s grip harder. Without this film, a frog dries out and suffocates within hours.
The venom glands form the second system. In toads (family Bufonidae), they form visible bulges behind the eyes, the parotid glands. They secrete a mix of molecules called bufotoxin, which includes bufadienolides, cardiotoxic steroids that act on the sodium-potassium pump of heart cells [Wikipedia] . A predator that bites a toad quickly feels the effects: hypersalivation, vomiting, heart rhythm disturbances. Humans can be affected through simple contact with mucous membranes.
The most extreme example is the poison dart frogs of tropical America. Their skin concentrates batrachotoxin, a molecule of exceptional potency that irreversibly blocks the sodium channels of nerve and heart cells. These frogs don’t synthesize the toxin themselves: they produce it from arthropods they consume in their natural habitat. Individuals raised in captivity and fed differently are harmless.
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