I think the main disconnect here is that what is "out of the ordinary" is, by its very nature, context-sensitive and subject to change across time and space, big and small.

Someone speaking at a loud conversational volume is out of the ordinary in a library, but not at a county fair. And that's not just a function of contrast with the existing volume level -- an audience member speaking loudly is still out of the ordinary in an otherwise loud auditorium (like a lecture hall, stage theatre, movie theatre, etc).

Likewise, someone whispering in the library may not normally catch your ear, but if they whisper your name, it may be very attention-grabbing for a split second. Once you realize that they know someone else with your name, though, you'll habituate to that stimulus, come to expect it, and probably ignore it. If someone else walks in and says your name, that may grab your attention again or not, depending on whether conscious processing is invoked to determine whether the new person is expected to belong to the category of "people saying my name", or the new category of "people over there talking about a friend with the same name as me."

Each part of this involves making countless assumptions (read: predictions) about what is happening at every level of abstraction.

Hell, even speaking of grass, this actually happened yesterday: I hurt my foot on a piece of metal that was the same color and height as a surrounding lawn. Roughly speaking: the metal would not have triggered a meaningful signal in my low-level color sensors, contrast sensors, edge detectors, or motion sensor pathways, and did not pattern-match any higher-level conceptual threats, so it did not violate any important background predictions about what parts of a lawn are safe. Ouch.