Blue eyes definitely go cross-eyed trying to focus on Levi's finger, and there's a moment of definite confusion, and then it clicks and-

...there's a brief, crestfallen expression that takes over. It's definitely not the first time someone's tried to make fun of his eyebrows, though, so a moment later, a smile takes over again, if somewhat more reserved than earlier. Erwin opens his mouth to say something, but then the other boy seems suddenly afraid of the firefly that's crawling its way closer to his skin.

"It's okay," he says kindly, and holds out the jar for Levi to take. If he doesn't, Erwin will tuck it between his knees before reaching out with both hands to coax the firefly off of Levi's shirt and onto his palm. He holds it between them, the little light glowing as though just for them.

"It won't hurt you, see?"