Why does he bite his nails?

Everytime he sees me he bites his nails and looks at me. And today when I saw him he was biting his nails like crazy while looking at me from his car. He definitely beams smiles at me when he thinks I'm not looking and he finds ways to be near me but when I look he acts like he doesn't notice me but the moment be thinks I can't see him or am distracted his whole face beams a big toothy smile. Why does he bite his fingers literally everytime he sees me though? Like today he was doing it intensely.

Why does he bite his nails?
Post Opinion