A horse with its tongue sticking out of its mouth, and seemingly unable to get it back into its mouth, is a rare thing. This could result from actual swelling of the tongue, due to ingestion of an irritating compound or toxin, or a traumatic injury to the tongue.

Weakness or paralysis of the tongue may also result from neurologic dysfunction at the level of the brainstem, or the nerves that control the muscles of the tongue. Horses with botulism can present this way, and immediate treatment is vital. Horses with severe infections of the mouth, head and tongue itself may also not be able to retract their tongues.

Horses that are severely debilitated can also show this sign. Strength of the tongue muscles is an indicator of general muscle strength. Old horses that have lost their front (incisor) teeth tend to stick their tongue out between their lips.