The seemingly tedious task also requires stamina - and facial muscles and a hand of iron.

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His face took on a masklike quality as the facial muscles became rigid.

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At the same time, the recipient would have to have their face, facial muscles, skin and subcutaneous fat removed.

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Devauchelle said most of the facial muscles of the recipient were preserved and it was mostly a question of attaching the donor skin and nerves.

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Mel Gibson, looking truly terrible (with sagging facial muscles and a listless body), is Walter Black, a prosperous suburban businessman who has fallen into an alcoholic funk.

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By stretching the inside of the cheeks of several patients who have complete facial nerve palsy with a finger, while performing routine checks for ulcerations or trauma, Ms Clapham caused the paralysed facial muscles to move - something not seen before.

BBC: Facial palsy patients helped by mouth massage

But to reach the physiological root of those sensations, we need to take a close look at the vagus nerve -- actually a bundle of nerves that starts at the base of the brain and branches out through the body, linking up with the facial and vocal muscles and the heart, lungs, and gut.

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Because Boxtox injections freeze the muscles of the face, they also inhibit our ability to mimic the facial expressions of others.

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Facial paralysis can be caused by damage to nerves through injury, surgery or unexplained syndromes, which make muscles to weaken and droop.

BBC: Facial palsy patients helped by mouth massage