Oh...kay. Tadashi wouldn't personally pick these circumstances to start teaching someone about medical care, but he wasn't the guy with actual training, so he meekly headed for the supply cabinet and tried to work out the answer without relying on the books in his head.

It didn't work, but he felt that he could make a decent argument in support of his choice that wasn't "that's what the magic told me". He retrieved the Hibiclens and moved back to the table.

"Water and saline would work in a pinch, but something with actual cleansing power would be better," he explained, offering it to Brainy and trying not to sound like he was spitting up a textbook. "And peroxide and rubbing alcohol are way too harsh."