How do you know it isn't magical self-cleaning glass? Or perhaps they have glass robots to do it all.

[Being in the middle of a warzone isn't all that new to Loki, and right now he can't hear too much going on, so he's willing to divert her attention for a little while, away from any inexplicable weakness.]

I think you have too much faith in me. Besides, she'll be fine there. Nothing is getting through those bindings any time soon.