ὑποψοφέω · hypopsopheō — LSJ
make a slight noise, ἐν τοῖσι ποτοῖσι Hp. Coac. 62, cf. Epid. 5.63; of water under ice, Ael. NA 6.24.
ἐπορχουμένην ἑαυτῇ . . καὶ τοῖς δακτύλοις . . ὑποψοφοῦσαν snapping her fingers in accompaniment, Plu. Alex. fort. 2.336c.