"I'm not sure if that's a good idea. It's a good thought but-- if it does flee, who knows where it'll go. We wouldn't want it to put anyone else at risk, right?"

Deep down inside, Armin is still a soldier. To protect others was (partially) why he joined the corps and then later the scouts.

"Right now, we just need to keep it here for as long as we can until Louie returns. Try using Yawn again to put it to sleep. Even if it doesn't last, it'll buy Louie some extra time!"