His strange habit makes sense when you consider that he's an environmental scientist who studies how to reduce litter, including things that fall off garbage trucks as they drive down the road.

他是一位研究如何减少垃圾的环境科学家，其中包括研究减少垃圾车行驶时掉下来的东西，当你考虑到这一点，自然就能明白他为什么会养成这种奇怪的习惯了。