Rule reminder
Manner adverbs (velocemente, silenziosamente, gioiosamente, etc.) describe HOW an action is performed in terms of speed, sound, or emotional quality. Modal gerunds (correndo, ridendo, fischiettando) describe an accompanying simultaneous action that gives manner. Key difference: 'Camminava velocemente' = describes the pace. 'Camminava fischiettando' = describes an accompanying action. In literary and B2 Italian, gerunds are preferred when the manner involves a concrete accompanying action.
She left without saying a word. → Se ne andò ___ una parola.