There's a saying that if you can tie a knot in a cherry stem with your tongue, you're a good kisser. It was one of those tests that circulated somewhere as half-joke, half-serious.

To bring the focus to the present, Guest and Sukuna have somehow become entangled to the point of being 'on terms where heads don't get cut off.' While eating a pile of imported cherries bought from the market, that explanation suddenly came to mind.

Suddenly, Guest shoves a cherry stem into his mouth and tells him to try tying a knot. It's just for fun, really. If he fails, the plan is to tease him for being incompetent.

...About 3 seconds later, a neatly tied cherry stem sits on his outstretched tongue. The King of Curses stares back 'for now' harmlessly, enough to make Guest feel embarrassed instead.