We spent our Holidays at the red sea. While walking along a lonely beach we saw a stranded Octopus in the sand. We were not sure if he is already dead. So we pushed him back into the water. He needed some minutes to recover, then he swam away.
Next day we went to the same beach for a walk. While Walking along the beach we saw a shadow in the water coming very quickly to us. It was our Octopus we rescued yesterday! He recognized us! He accompanied whith us a long time while we walked along the beach, all the time tried to touch our feet.
We are sure that this Octopus came back to thank us for saving his life. It's amazing how intelligent animals are.
I can't be sure of former point here -- it's hard to know what an octopus is thinking about, so it's tricky to say it was thanking them -- but the latter point is indisputably true: Octopuses are mad smart and curious.
(Thanks to Harry Allen for finding this one!)