You've probably brushed your shoes up against them from time to time just because.

你可能时不时地把鞋子碰到它们， 只是因为。

One moment Mr Micawber looked extremely miserable and depressed, the next he was brushing his shoes and singing a song before going out.

忽儿，米考伯先生看上去极其痛苦、消沉，忽儿，他又会边擦皮鞋边哼哼小曲儿准备外出。