First of all, it’s the motion that gets the attention. It has to do with “rods” and “cones” in their eyes. Deer see motion better than they see detail. They see better at night than we do for the same reason. Regarding the tail: you’ve seen 2 dogs meet, and what’s the first thing they do? Smell the other’s rear! A lot of information is gathered this way in the animal kingdom. You might call it the “business end” of animal interaction. The motion provided by Tail-Wagger is the “at ease” signal. An alarmed deer would not wag their tail in this manner. If you watch deer enough, you’ll notice that they often give this “wag” right before their head goes down to eat. The “ear twitch” is another matter. At the right time it might be OK, at other times, it might be a mistake. Why chance it?