The bug
The player's shoulders shake aggressively if in a minecart with a lot of other minecarts occupying the same space.
Steps to reproduce
Place a bunch of minecarts on one rail
Get in one of the minecarts
Go in front-view third-person mode
Move your screen around at different angles until the player's shoulders start to shake without your control.
Lots of minecarts aren't needed to reproduce this issue, therefore, making this ticket a duplicate of MC-230788.