One of my closest friends had a Goldenx who was wearing his collar and tags in the yard while her Mom was home... he slipped through a hole under the fence, and his collar was snagged on the fence. He was hit by a car on a nearby street before her Mom even realized he was gone. They later found out that AC had picked him up, and because he was badly injured and had no tags or a microchip they euthanized him on the spot.
That is heartbreaking.