Rats cause a client crash if somehow ridden and make the world unusable. Any entity can be used to cause the crash.
Steps to reproduce:

1. Execute the command below

• /summon caverns_and_chasms:rat ~ ~ ~ {Passengers:[{id:"minecraft:chicken"}]}
• This command will summon a rat with a chicken riding it, which as a result will crash the game.
  Crash Report:

crash-2025-03-09_15.10.37-server.txt

Only Caverns and Chasms 2.1.0 Beta 1 and Blueprint 7.1.2 were loaded.