From Longman Dictionary of Contemporary Englishmobile mouth/face/featuresmobile mouth/face/featureswrittenEXPRESSION ON somebody'S FACE features that can change their expression quickly His mobile features registered amusement. → mobile
Examples from the Corpus
mobile mouth/face/features• He finds a woman in black lace, with piercing eyes and a mobile face.• They did not show emotions as plainly as more mobile faces did.• I finally found Martin Clunes, the most mobile mouth in show business, lurking behind a large moustache. 