<unk>  is a bodily function in animals that occurs primarily in response to cold; the jaw muscles begin to shiver leading<unk>  to crash together. It may also occur as a result of bruxism where emotional stress causes the jaw movements. Certain medications can lead to<unk> <unk>  as a side effect, especially antipsychotics and SSRIs.
Chattering teeth
Shovel-shaped incisors
Black hairy tongue
Spotted lunulae
Crenated tongue
Macrodontia 
Coarse facial features
Asymmetric crying facies