Severus couldn't help but give her a look. He had to force himself to back bite his initial reply (too large; perhaps you should start with Potter's brain) and instead decide to keep it civil. After all, Potter wasn't here, and there was no point in pushing her away just as they were starting to get somewhere.
"I was thinking that you might like to start with a glass of water," he said. "It seems sort of pointless to freeze something already frozen, yeah?" It was as close as he could get to teasing, especially since he managed to say it without a hint of sarcasm in his voice.