It startles them into movement--Frisk steps forward, starts to snatch out to snatch Chara's hand away from the flowers. But they stop and flinch back partway through, knowing full well the reaction that would bring.

The bright red blood stands out against the green and yellow and Frisk's eyes are fixed upon it for several long moments before they reply.

"I...I wasn't the one that brought you here. I called, but...you didn't answer, then."

Or maybe it just took them this long to come.

Frisk's hand lifts again, but this time to point behind Chara to the flickering portal behind them. "It's...these things. They steal people from all different kinds of worlds, 'cuz they're broken. No one could get them to work right."