Half-smart? [She gives him a look that could melt his face. She usually reserves those looks for Kyon.]

Okay, the term is "dumb" or "stupid". But it actually makes sense that the Shadows are dumb. They're lower-level in the hypothetical monster organization, right? The top-tier monsters are sending out the shadows to do their dirty work. But since the Shadows aren't that bright, they're given minimal tasks, like causing mayhem and attacking us. But they're alot of them, so if they get killed off it doesn't matter.