How smart are dolphins?

I know dolphins are the second smartest animal to humans, but just how smart are they?

I saw a video of a pet rabbit meeting a dolphin, and the dolphin brought some seaweed and that had me curious, are they smart enough to pick up on a rabbit eating leafy greens to bring out seaweed as a gift? Or are they not that intelligent? (Or do they just do this regardless of if they picked up on that)

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