We have a dogsitter when we are on trips. According to her, our heeler would politely take blueberries that were offered and then wander off, returning not long after. It was only later that she found a stash of uneaten blueberries on the couch. My little man was a desperately skinny and frightened stray in a kill shelter before he came to us, and on the theory that whatever makes him feel safe and content is better than the alternative, he's, uhhh, put on weight. If he liked the blueberries, they would not be left on the couch.
The fact that he was a stray could explain that behavior. He may have had a bad experience with wild berries and didn't want to get sick but also didn't want you to feel bad.
Yeah, we always wonder what he had to deal with. He's still very sensitive to any pressure at all on his ribs, and he hoards soft toys in a den (under a bed), though he responds with exasperation rather than anger if one is taken. When we first got him, he tried eating acorns (hell on a dog's stomach, I understand), pre-emptively winced the first time he barked in view of me, and despite generally hating to go outside any longer than it took to potty, climbed up on our patio furniture to investigate the fence the first time we had to leave him with a sitter.
These days, he's fat, which is a negative of course, and he's still an idiosyncratic homebody, but he's also confident enough to ask for affection, isn't reactive to anything other than vacuums, and has a great relationship with our other dog. The turnaround has been lovely, and if being a chonk came as part of it, I think it's a trade worth having made. Our other rescue was born after his mother arrived at the foster, and has a very different relationship with food, exercise, and new people. His super playful but emotionally aware energy has worked well with our "seen some shit" heeler.
I read another comment that the vacuum seems like a loud animal yanking you around, and the solution is to drag it into the middle of a room and shout at it a bit in view of your dog