He's seen Mako in serious panic mode. It's a bit scary and usually results in everyone else (minus Haru) around him panicking, too. Luckily this isn't so bad, even if it's still pretty damned unnerving and upsetting for both of them.

"... oh! Right, I do! It's--!"

Nagisa attempted to move towards the nearby end table, but his movements only got him about an inch forward before he dropped face first on the florr.

"... in there..." came the rest of his muffled line, finger pointing at it.