Chase does not, in fact, understand, but from talking to other species of people here, that's actually commonplace for him now.

A human turning into something else is something he knows a thing or two about, but...not like this.

"What didn't you think?"

As he says so, he increases the pressure on his arm, to get Eiji to sit down. He doesn't know much about the sensory loss, but what he does know is that Eiji probably shouldn't remain standing.