Press each key and check it returns quickly under spring tension without sticking, and check that connected key clusters move in sync, since a bent key rod or misaligned linkage is common after a drop. Check every pad for a light-tight seal by holding the flute up to a light source with each key closed. Inspect the body, especially the headjoint and footjoint tenons (the sliding joints), for dents or looseness that would prevent airtight assembly. Check the embouchure hole edge for nicks or wear, since this directly affects tone response and is easy to overlook compared to the more obvious keywork.