I see a change in the code that looks like it might allow mobs to turn faster/sharper (old code limited the yaw in what MCP calls EntityMoveHelper (and also GuardianMoveHelper and SlimeMoveHelper) to 30, new code increases that to 90). But I'm not sure how to actually test it, so I didn't add it. Anomie x (talk) 23:32, 9 December 2015 (UTC)
Regarding the new sound assets
Just a reminder, sound assets aren't part of the snapshot itself - they are updated separately at the release of the new snapshot. This can easily be confirmed by launching 15w49a/b as well, the new sounds will still download and play in-game.
Additionally, it seems there are no sound assets yet for entity.snowman.ambient or item.bottle.fill_dragonbreath. There are no such sounds playing in-game, and the launcher console is complaining about missing sounds:
[00:56:02] [Client thread/WARN]: Missing sound for event: minecraft:entity.snowman.ambient
[00:56:02] [Client thread/WARN]: Missing sound for event: minecraft:item.bottle.fill_dragonbreath