Years ago, my sibling's dog became suddenly sick after being petsat for a week. The dog was trying to vomit and poop but nothing came out and was in distress. He was taken to the ER and they stabilized him but wanted to do a bunch of invasive tests for every possible thing. They had no clue as to what could be wrong.
My sibling called my mom's vet in the morning who said to bring the dog to him for exploratory surgery. When they arrived, the vet was at the front counter. He looked up, saw the dog and said "you didn't say he was a lab. He ate something. I'll go in and remove it and he'll be fine."
One surgery later, the dog had swallowed an oak gall. The gall was blocking the intestines and poisoning the dog.
Dogs don't always do the smart thing.
