Skepticism, suspicion, or 'wait, come again?' — the single raised eyebrow (borrowed visually from the Spock/Vulcan look) reads as doubtful scrutiny rather than open hostility. Its name internally, 'Mr. Potato Head-ish' at proposal stage aside, it's become a favorite for calling out something that doesn't quite add up.
Keywords: disapproval, disbelief, distrust, emoji, eyebrow, face, hmm, mild, raised, skeptic, skeptical, skepticism, surprise, what