[Later, Sans won't be able to say exactly when it happened. He has no plan to touch the relic, no plan to get any closer to it than he needs to. It's somewhere in there, moving around and preparing to magic the book into Sans's dimensional box, that suddenly the relic is all he can think about. It's too fast for him to even be alarmed. The world is distant, but he knows the important bits of what's happening; he knows Mira is going to drop the relic in a moment. He knows he can reach it. He doesn't think to grab it, grabbing it is an inevitability. He wants it, so--
the part where they actually retrieve the relic
And there it is, in his outstretched hand.]