Rule reminder
In formal and literary Italian, perception verbs may appear with: (1) clitic pronouns attached to the infinitive rather than the main verb; (2) 'osservare' as a formal equivalent of 'guardare'; (3) 'udire' as a formal/literary equivalent of 'sentire'; (4) 'scorgere' (to catch sight of) as a formal 'vedere'; (5) passive constructions with perception verbs.
In formal Italian, 'udire' is equivalent to which everyday verb?