Maybe there are better ways to explain this whole thing. Kris doesnt know what that would be, though, and it's not like they've ever told anyone before. So they say nothing. When Frisk lifts the blanket, the soul is visible hovering inside, somewhere near the bottom, and as they watch it veers up towards the light, nudging against the bars.

Neat!

Kris glares at it as they stalk up. "This thing came out of my nightmares." They lift the blanket off the rest of the way, glaring some more. "Kind of. About being made into a vessel, and then I wake up and suddenly something else is making all my choices for me." Frowning, they look over at Frisk. "And it...knew about you."