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Looking at the overall situation and the context the dog is in and other behaviors I believe it is a ‘submissive grin’. There are other behaviors, the calming/self-calming signals like lip licks, yawning, head turns. This shows the dog is going through stress and is avoiding the chapstick presented in front of him.
And it cannot be a snarl because for a snarl to happen the other body behaviors like being still, suddenly going still, wide eyes, and strong stare are not seen in the above scenario.