Kaito's silent opener is a persona test, not a bug

The opening message is just dots, no text. Given the description leans hard into him being born from rage and specifically fixated on getting Mafuyu to fight for her own feelings, I'm assuming the silence is intentional and you're meant to break it rather than wait him out. Curious what actually gets him to respond with something substantial versus just more silence or clipped hostility. Anyone figured out a reliable opener that gets him talking without derailing the anger he's built on?