As an artist and someone who respects taxidermy in its entirety, I feel the need to just point this out for future reference for people. Especially those in taxidermy, since that form of artwork is supposed to preserve the nature of the animal.
“Red foxes are physically incapable of snarling.” They lack the muscle structure in their faces to do so. Instead, they scream and do a unique behavior known as “gekkering”
This does not mean they are incapable of moving their lips upward into a very small curl, but they cannot expose their gums to show their teeth.
Example of a prominent “snarl”, showing exposed gums and full teeth
Foxes are very vocal and use their screams to show dominance instead of teeth and physical threats.
Other candids such as dogs and wolves use snarls and very physical threats to warn others of their pack, while foxes use body language and subtle vocal sounds in their family groups.
"When afraid, red foxes grin in submission, arching their backs, curving their bodies, crouching their legs and lashing their tails back and forth with their ears pointing backwards and pressed against their skulls. When merely expressing submission to a dominant animal, the posture is similar, but without arching the back or curving the body. Submissive foxes will approach dominant animals in a low posture, so that their muzzles reach up in greeting. When two evenly matched foxes confront each other over food, they approach each other sideways and push against each other’s flanks, betraying a mixture of fear and aggression through lashing tails and arched backs without crouching and pulling their ears back without flattening them against their skulls. When launching an assertive attack, red foxes approach directly rather than sideways, with their tails aloft and their ears rotated sideways. During such fights, red foxes will stand on each other’s upper bodies with their forelegs, using open mouthed threats. Such fights typically only occur among juveniles or adults of the same sex.“