Arm movement is client side when you are on a Lan world.

What I expected to happen was...:
Arms would move when breaking blocks.

What actually happened was...:
Arm movement is client side and you can only see your arm movement, not the other player(s).

Steps to Reproduce:
1. Go to a block (all blocks work).
2. Break it with your HANDS.
3. Have another player watch you whilst you break the block .