"Oh, I see," Usopp answered, although he was curious what the uniforms looked like. And really curious why Sai was showing his belly off. If it were Nami or Sanji, he'd assume fashion, or in Nami's case possibly an attempt at manipulation. If it were Zoro he'd assume his clothes shrunk for some reason or had been cut and he just hadn't noticed. Luffy, he'd assume his stomach had been hot for some reason. "Does your stomach get hot a lot?" That was the only one he could imagine Sai relating to--purely physical comfort but not outright cluelessness.

As he saw the headband better, he grinned, but slowly, not quite sure of himself. He'd been a bit sad to see his hand-made gift replaced, but had decided to brush it off (after all, he'd gone back to wearing his own headband at night.) "You don't have to wear it if you don't want to." Hadn't he said that before?