Claws clang as they meet blade- if she didn't back down from being hurt that badly, there's no way a second opponent was going to force her to. Demona is evidently a bigger fish- stronger and more vicious than Darcy.

It's a good thing he learned the strength in teamwork early on.

"I don't even fucking breathe-"

So when Darcy retaliates, Demona might think it's aimed at her, but it's not. He's trying to trap a hand between his blades, leaving her open for Venom.