I've noticed that they do something none of the other horses do while I'm grooming them. While I'm at their side (usually after I pass their girth line) they will tip their noses toward me, looking at me straight on, and stare for about ten seconds before looking forward again. They do this on both sides while I groom, and will do the same when I bring the tack.
Does anyone know what this behavior could mean? It's not aggressive or dominant (they don't nudge, push, pin their ears, or try to bite), but none of the other horses (even the severely passive ones) exhibit it.
I'm simply curious; it's not a dramatic, concerning behavior but it is rather strange to me.