The dog scratched itself behind the ear.

狗用爪子挠挠耳后。

《牛津词典》

He is holding a thick book in his mouth. A red pen is hidden behind the ear.

他口里叼着一本大书，耳朵上夹着一支红笔。

youdao

The most barren region was behind the ear, with a median diversity of 15 species. In comparison, the forearm teemed with a median 44 species.

细菌贫瘠区时耳朵背面，细菌种群的中位数是15，而在前臂是44。

youdao

She went over to check it out and found a big red lump behind the ear.

CNN: But is it really an emergency? When to take a child to the ER

The MDHearingAid also sits behind the ear with a plastic dome in the ear canal.

WSJ: Testing, Testing...Can You Hear Better Now?

The Bonebridge is surgically fitted under the skin to the bone structure behind the ear.

BBC: bonebridge