Why do mice cry red tears?

Owners of rats and mice may be surprised to discover their pet rodent has scarlet tears and nasal secretions. Red crusts can form around their eyes and nose, and their forepaws can turn red from touching their faces. This redness is induced by the release of a red pigment called porphyrin rather than by blood.

This pigment is produced by the Harderian gland, which is located behind the eye. (Chromodacryorrhea is the scientific term for colored tears.) Although crimson tears are not blood, they do indicate that your pet mouse is sick since they shed these tears when they are sick or agitated.