Bechorot 39 - Eye Exam for Firstborn Animals
How does one check whether the condition of watery eye that obstructs the view is indeed a permanent blemish that won't heal? One needs to feed the animal first dry fodder (meaning, grown in dry months), then moist fodder (grown in moist months), coming from rain-watered fields, for three months, not in any other combination of factors. If the condition still persists, it is a sign that the blemish is permanent.
How much fodder has to be administered? - The volume of a dried fig. Should it be given at each meal or at the first meal? Before the meal or after? Before drinking or after? Should the animal be fettered or free to roam, in the city or in the field, and if in the field, is a garden next to the city good enough? All these questions remained unresolved.
Blemishes of the nose: if it was punctured, notched, or split, and the same for the lip. Qualifying blemishes of the mouth: front gums notched or cut, back gums completely uprooted. Rabbi Chanina ben Antignos says: "Gums from the molars and beyond are considered hidden blemishes and are therefore never examined, gums under molars including."
Art: Gerrit Van Honthorst - The Tooth Puller