Place this clip in the middle of a scene, just after the line that needs undercutting, then follow it with the Law and Order Dun Dun for a dramatic reveal, or open with the Windows XP Error Music when the excuse has already failed.
Über diesen Sound
This is a single cough lasting about three seconds, a brief human sound with no words attached. It feels awkward and faintly comic, like an interruption nobody planned, and works as a deadpan reaction to an uncomfortable pause in a conversation.