I'm here again, with another page that… well, you know! ;)
Hayate finally ‘tastes’ Hitomi's essence which we all know isn't a tangible thing. But why his eyes turned dark? The essence is like your trademark, Hayate (and the other vampires) use his senses to detect it and, if he likes it, he can track it anywhere. Like a personal GPS :D
Oh, also there's an important thing (at least for Hayate) that Hitomi mentions in Chapter 2, we'll se what is it in the next page so, see you on Sunday!