Land frogs can withstand the heat of summer, but die if exposed to rain. Water frogs, when overheated by the sun's rays, dip into a fountain to cool off. Frogs can be green or red, and have a croaking voice that they use to attract a mate. They produce the sound by inhaling to inflate their sides, then compress them to force out a croak. Their eyes shine like lamps. If the bone from the right side of a frog is dropped in boiling water, the water cools and will not boil again until the bone is removed. Its body is full of medicines and poison; while feeding it ejects both, but takes back the poison as a weapon.

Various authors class the frog as a serpent, a fish or a worm. Thomas of Cantimpré in his description of the frog first says it is a worm, then quotes Aristotle to say that it is a fish.

In some cases the description is specifically about the toad, which is here included with the frog. Toads were considered to be poisonous.

If the tongue of a water frog is placed on the head of a sleeping man, he will talk in his sleep and reveal secrets. Some say this will also happen if the tongue is cut from a live frog a placed over the heart of a sleeping woman. Ashes of a burned frog in a bath will remove body hair. If a bone from the right side of a frog is dropped into boiling water, the water will cool and will not boil again until the bone is removed. Their ashes drunk in water is a remedy for the poison of the sea-hare. If the frog called corriens is thrown into a dog's mouth the dog will be unable to bark.