Thor tilts the mouth of his bottle towards Loki.

"If you're up to something usual, then you're up to no good." Thor gestures to his eyes, then gestures at Loki. "I've got my eye on you."

He cracks a smile at his usage of the word eye. If you're going to spend the rest of your days with one eye and one synthetic one, you might as well be good-humored about it.