A similar but unrelated behavior , wood - chewing or lignophagia , is another undesirable habit observed in horses .
Habit does not involve sucking in air ; the horse simply gnaws on wood rails or boards as if they were food .
A similar but unrelated behavior , wood - chewing or lignophagia , is another undesirable habit observed in horses , but it does not involve sucking in air ; the horse simply gnaws on wood rails or boards as if they were food .