Place it at the entrance beat in your edit, right after the newcomer appears on screen and before any response shot. Follow it with a SpongeBob sad song underneath the next shot to extend the beat, keeping this line first so the pairing reads as reaction then fallout.
关于此声音
A one-second voice clip of the line 'what are you doing here' delivered in a flat, sad tone. It lands as deflated and a little hurt, like the speaker was not expecting company and does not welcome the surprise, which makes the brief question feel awkward and quietly disappointed rather than angry or confrontational.