At long intervals, he drew his thumb along the edge of his knife, and nodded his head with satisfaction.
每隔很长一段时间，他就用大拇指摸摸刀刃，满意地点点头。
2
The edge must slice his thumb because his hand flies to his mouth, and he's sucking hard, eyes wide open.
纸片一定是划到他大拇指了，他的手里刻缩了回去，嘴用力吸着大拇指，瞪大双眼。
3
Practice with how much pressure needs to be put on the razor or if the thumb should hold hair against the razor's edge are each part of experimenting with this type of thinning out of hair.