Odor--delivery trucks burn unusual fuel
Mind reading--dogs sense intent to deliver
Yes, the postal trucks do. But UPS uses plain old vans -- well, delivery type, with an open-sided step-out type of cab. I don't know what their engines sound like. Never paid attention. You may be right about that. But the dog could spot them through a closed window, and the street is at least 50 yards in the distance. Well, if I can hear the traffic -- and I can -- I'm sure the dog could. My point was that loads of trucks pass by, many of them are delivery-type (I guess), but only FedEx, UPS, and the mail trucks got her attention. Thus I assumed it was the colors that the dog had learned to recognize, and those colors became associated with visits from such trucks. Anyway, it wasn't because of any visual clues from me. It was the dog who clued me in when one of those trucks was passing by.
Which has very little to do with red bones in caves ...