Collecting, throwing, and placing snowballs work in multiplayer!
Snowballs have five states: "carried", "thrown", "synced rigidbody", "placed", and inactive. Transitions between these states are now successful across the network.
When thrown, snowballs move more smoothly than furflies, as their trajectory is deterministic and thus does not need to be synchronized until they hit an object - at which point syncing resumes.