Eyebrow

The eyebrow was an area of hair located above the eye. Raising an eyebrow was a common method of showing interest, (PROSE: Christmas on a Rational Planet, The Eyeless, et al) so much so that there was a raised eyebrow emoji. (TV: Smile)

Due to an incident in the War in Heaven involving the Fendahl Predator, (PROSE: The Taking of Planet 5) the Delphon communicated using only their eyebrows. (TV: Spearhead from Space, AUDIO: The Havoc of Empires, et al.)

Upon learning that the Eleventh Doctor had shaved his head, Clara Oswald questioned if he had shaved his eyebrows as well only for him to self-consciously defend them as "just delicate". (TV: The Time of the Doctor) The Twelfth Doctor by contrast was noted to have very large "attack" eyebrows, (TV: Deep Breath) with even giving him the nickname "the Eyebrows". (TV: The Witch's Familiar)

Romana II asked the Fourth Doctor why the Mona Lisa didn't have any eyebrows. He started to chide her for asking this, but then realised for the first time that the Mona Lisa didn't. (TV: City of Death)