In 2015 my neighbor and I brought home puppies from the same litter but picked them up a few weeks apart. They got theirs first and told us there was one more puppy. Eventually we adopted her.
My neighbor and I swear that they play with each other differently - possibly because they remember each other. And when a third dog from the litter came over, it was absolutely clear to us that they were thrilled to be reunited.
This is so amazing!
Here's a TV news story about it.