Chewing on leather
From www.leather-dictionary.com - The Leather Dictionary
Some animals, such as horses or alpacas, are occasionally observed chewing of leather, for example leather straps. This habit is interpreted by veterinarians in such a way that the chewing is stress-relieving and soothing. Furthermore, the chewing process - similar to the chewing gum in humans - increases the salivary flow so that the acid-base ratio in the mouth better compensates and caries is pre-diffracted.
Video about a leather chewing alpaca.
Additional information
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