Spangle's a chital, and like all deer, chital shed their antlers annually. Though unlike most deer which folks tend to be familiar with (red deer, fallow, white-tail, etc), which are temperate deer, chital are tropical deer. Temperate deer shed their antlers at the same time each year, while tropical deer change their schedule a bit, and don't always line up with other deer of their own species or herd.
All this is to say, that Spangle gets startled when his antlers shed each year, he never seems to expect it!