He quickly threw his underwear into the washing machine, afraid someone might notice the skidmarks.

skidmarks 是复合名词，由 skid（打滑、滑行）和 marks（痕迹、印记）组成。skid 原指车辆打滑留下的痕迹，这里比喻性地指内裤上留下的污渍痕迹。skidmarks 特指内裤上因排便残留物或分泌物留下的黄褐色痕迹。