If you give mobs a high speed boost effect (I set it at level 50) they will soon begin running in steady rectangular patterns. The size and dimensions of the rectangles vary.
How to re-create:
go to an area full of mobs
type /effect @e[type=!Player] minecraft:jump_boost 10000 50
wait a few seconds
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Sonicwave
migrated
Note: this also happens when villagers start running to get inside at night, with NO extra speed effects applied.
Sonicwave
That's MC-15080.
Unfortunately, effect amplifiers beyond 4 are not supported.