There was a bug in the game where if you break a block under another one you can through the floating block and see caves but if you go to far in the block you then start to take damage.

Thank you for your report!
However, this issue has been temporarily closed as Awaiting Response

Is this still an issue in the latest version? If so, can you please add it to the affected versions (or mention it if you are not the reporter).

Also, just a reminder, to make your bug report as effective as possible, please try and include the following steps to reproduce the problem:

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Observed Results:
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Expected Results:
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📓 Issue Guidelines – 💬 Mojang Support – 📧 Suggestions – 📖 Minecraft Wiki

Cleaning up old tickets: This ticket had been set to 'Awaiting Response', but has not received a response from the reporter (~3 months+) so is being closed as Incomplete. If you feel this is still a valid issue then please comment, or create a new ticket following the Issue Guidelines which includes steps to reproduce the problem.

Quick Links:
📓 Issue Guidelines – 💬 Mojang Support – 📧 Suggestions – 📖 Minecraft Wiki