Yussa gives Caleb an amused, fond look. A smile just shows in the curve of his mouth.

"Flatterer," he says warmly. "I think it might have been a component I found there that reacted badly. One could argue that was certainly a kind of... vigor."

He'll have to go through his notes more carefully. They are meticulous and he is certain he wrote down exactly what he did - or what he was planning to do - before he did. There is the chance he did, and if that is the case... well. He knows that Caleb is rather clever in working backwards from a result. With him here, it shouldn't take too long to sort out what went wrong and at which stage.