Stumbling into Brook didn't help when the former skeleton had had enough problems when he'd been a skeleton with just seeing himself in the mirror! The moment he saw the skulls being pointed to, his mouth fell well beyond the point any normal person's would or could and went back as well, right onto his butt.

"Skulls! There's skulls!" As if that wasn't obvious. "Why are there skulls?!" He pointed, demanding an answer that wouldn't come. Unlike Usopp, Brook didn't have enough sense to just look away and pretend he hadn't seen it, because he had eyes now so he knew what he could and couldn't see! And he saw skulls!