Not in this case. Like dropping a pebble in the water. Obvious to someone standing right there. There's no comment about that little hint and it strikes him as curious the vampire says nothing. Is it the blood? Is it a sense of morals? Neither rejection nor a sudden interest either. Does he not drink blood? Or is this a different kind of vampire? Dabi can't say he knows, since he's just going on base assumption. Probably rude, but hell if he cares.

Instead, he's left with a dismissive departure and Dabi watches as Mayerling vanishes into the night. Can't tell if he walks away or actually melts within the darkness.

Gonna keep an eye on that one...