Nail biting, thumb sucking, hair twirling, foot tapping.

爱咬指甲，吮姆指，绕头发，跺脚。

youdao

I thought the picture was fuzzy. I couldn't see whether it was a little sister or brother. But I could tell it was sucking its thumb.

我觉得这个照片很模糊。我看不出来是个小妹妹还是小弟弟。但我能看出来小宝宝正在嘴里吃大拇指呢。

youdao

The little boy was sucking his thumb.

小男孩儿吮着拇指。

youdao

Parents often wonder what effect thumb sucking or sucking on a pacifier might have on their baby's teeth.

VOA: special.2009.03.11

The American Academy of Family Physicians says most children stop sucking their thumb by the age of four.

VOA: special.2009.03.11

When people look at an unborn baby sucking its thumb, they see it as a human being, says Josephine Quintavalle, of Alive and Kicking, a pro-life campaign group.

ECONOMIST: Abortion

Apple is taking that supposedly wasted cash hoard and kicking serious ass while the rest of the computer industry sits around sucking its thumb and starts complaining about big, bad Apple cleaning up components and shutting them out.

FORBES: Apple Flashes Cash As Japan Supply Chain Woes Continue