The first time she crosses his view, it can be blamed on the room. Too crowded, too loud, somebody moving a chair, a friend pulling her past the bar.

The second time is different. She comes back through the same little strip of space with no obvious errand. Maybe she checks the mirror behind him. Maybe she reaches for a napkin she could have grabbed before. She does not have to look straight at him. In fact, she may make a point of not doing it.

That is the cover. If he noticed the first pass, the repeat gives him something to work with without handing him a signed invitation.