There are some behaviours that we humans do that seem to prompt imitation.
A few examples:
Whenever someone does one of these things around me, I feel a certain subconscious response that often goes unchecked and results in me imitating their behaviour. Someone laughs, I laugh. Someone yawns, I yawn. And so on. (To be fair, my attempts to not imitate puking have often been very successful.)
All of these things have something to do with the face. In particular, the mouth. All of them shape the lips and the mouth/throat in a very peculiar way or shape, that we can all recreate without much thinking. Too little thinking, perhaps.
Sometimes people use contagious as a word to group them together as if they were sicknesses or morbidities.
So are they just symptoms of something larger?
Laughing could be said to be a symptom of happiness. I dispute this on the basis that you can laugh when you’re sad and you can imitate a laugh or fail to resist it even though you “don’t feel it”. I’d say, it’s rather a symptom of wanting to fit in.
Yawning is a symptom of sleep, surely? No, since the one yawning could be sleepy, or in dire need of air. But the one imitating them does not need to feel the same need. Once again, it appears to be the want to fit in.
With emissus it is probably a symptom of a sickness. Not only probably.
Make of this what you will.