It's a little jarring, catching sight of a silhouette that's only really familiar in one specific way. That's the first thing that catches Shiro's eye, anyway, followed immediately by what the person's doing, which is a little alarming in its own way, but more just sparks his curiosity. It seems like an incredibly specific but not necessarily useful task to set oneself to.

"Good arm," he calls out, watching another purposeful, doubtless precise throw, hears the words that come out of his mouth a fraction of a section after they do, and is instantly grateful he's got his coat and shirt sleeves cuffed to where his elbow would be, if he still possessed one on the right side, which he demonstrably does not.