If you are inside a building or just under cover, picking up an item off the ground while it's raining outside will cause the rain to momentarily appear inside while the item enters your inventory.
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violine1101
Thank you for your report!
We're actually already tracking this issue in MC-163575, so I resolved and linked this ticket as a duplicate.
If you would like to add a vote and any extra information to the main ticket it would be appreciated.
If you haven't already, you might like to make use of the search feature in the future to see if the issue has already been reported.
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