Faeries often disguise themselves as toads, frogs or even mice, which can be dangerous as frogs and toads especially are often used in magic spells or cures.
This is taken from The Discovery of Witchcraft written in 1584
Frogs are also used to cure thrush: take a living frog and hold it in a cloth, put the head of the frog into the patients mouth making sure that it does not go down the throat. Hold it there until the frog is dead and then take another frog and do the same.
These are traditional cures from the fifteenth and sixteenth centuries so I am not advising that you should try them! And if they were really faeries in disguise I think they would be a little bit annoyed and remember never piss off a faerie!