Inside the booth
Make a silent conversation in a photo strip
Use looks and small reactions instead of speech bubbles.
Two people can suggest a conversation through their attention to each other.
Agree on four beats
Begin looking at the lens, turn attention toward each other, react and return to the camera. Keep the idea playful and comfortable for both people. Stay within the tested framing and avoid relying on tiny props or text that will be unreadable in a narrow strip.
Read it without explanation
Show the whole sequence to the participants and ask whether its rhythm is clear. An ambiguous result can still be enjoyable; do not force an invented argument onto a portrait. Keep any fictional caption clearly playful rather than presenting it as a real private conversation.