Last week, like every week with 3 grown sons in the house, we were playing parent taxi, and had to pick one son up from work, with about an hour or two's gap before we had to get another son from his work, which happens but not often. So we took the dog wiht us in the car and walked her before getting son 1, got son 1, then went shopping and came home to quickly unload before going back out to get son 2... We usually let dog back in the house if there's someone home to dog-sit and she's had her walk.
But just for once I said to husband "Why don't we unload shopping and just leave dog in the car, and she can ride shotgun with us back to pick up son 2?" I didn't even say dog's name (but then again I do call her 'dog' all the time so I think she thinks that's her second name)....
Whenever we get out of the car after dogwalking/son getting/shopping, she always jumps out of the car on her own, and runs into the back garden to wee (because why wee on a walk when you can wee in your own garden afterwards?) Then goes in the house.
But she sat calmly on the back seat, didn't even try to get out even though we left the doors open, and just waited til we came back to the car - only took us 5 mins, but we had a lot of shopping. She never does that. There were no conscious cues to her that we were letting her stay in the car, just me verbalising the idea...
She's not very intelligent either, so the thought she may understand more than we realise is a bit shocking.
When we finished unloading and got back in there she was, happy as anything. (She is never left alone - always with someone - rescue dog with 'issues' so doubly odd that she was happy to sit on her own and wait).