A little bit of Fluff on the top.

顶部有一点绒毛。

But from those simple bits of fluff, protofeathers became more complex over time.

但是随着时间的推移，从那些简单的绒毛中，原始羽毛变得更加复杂。

She was nervously picking bits of fluff off her sweater.

【pick】她紧张地摘着毛衣上的小绒毛。