Theo watched the thestrals and inclined his head slightly in Dean's direction to show that he'd heard the other student, but he didn't verbalise his reply. As far as he was concerned there were a lot of things far creepier than his fascinating thestrals and he didn't find them creepy even when they were aground.
He was broken from watching them as Dean shifted, turning to see the other boy rearrange and then start to draw. Theo immediately burnt with curiosity, but he quelled it (easily enough considering the punishments that particular trait had wrought him as a child) and continued to watch the flying creatures and the sun as it set; he could almost say that he was enjoying the comfortable, if not companionable, silence between them.