I was told dolphins are supposed to toy with dropped and floating items in the water.
They aren't doing this in my world.
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is duplicated by 6
Comments 4

Thank you for your report!
However, this issue has been closed as a Working as Intended.
This is a feature that is currently in the Minecraft: Java Edition snapshots. It has not made it into Minecraft (bedrock) in either the stable or beta release
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Reopened since the full UA was released since the creation of this report and now
Thank you for your report!
However, this issue has been closed as Invalid.
We're already working on achieving parity across versions where possible, and we're very keen to hear your requests or suggestions, so we'd encourage you to make a post at https://feedback.minecraft.net, or upvote an existing topic there. (Such as https://feedback.minecraft.net/hc/en-us/community/posts/360041803052--Java-Parity-Dolphins-New-To-Play-With-Items-On-Bedrock)
If you're not sure whether your issue is a parity request or a bug, hopefully this article will help explain further: Parity Request Guide
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📓 Issue Guidelines – 💬 Mojang Support – 📧 Suggestions – 📖 Minecraft Wiki
Confirmed on Android LG Q6. Bedrock 1.4.0.5. Items dropped into water do not result in dolphin interaction. New world generated with 1.4.0.5. Same with all dolphins encountered. Dolphins also not able to be fed. No prompt when holding raw salmon.