Guardian notices very little of this. They have a knack (or a habit, or a curse,) for letting their world shrink down to what's right in front of them, and right now, they only have eyes for Gaster.

But the skeleton's words actually get something like a snort from them, short and derisive. "I know. Doesn't mean it doesn't matter." They press on. "I can leave, if you want. But I'd like to stay. You shouldn't be alone."