The splashes that things make when entering/exiting the water are handled locally by the
player's cog. So when an actor, player, projectile, etc. enters/exits the water, the splash
message is called in the player's cog (usually kyle.cog) to create the splash.
Anything with the 0x20000000 Thing Flag will create a splash.
Sender
The thing that's splashing.
Source
Will be 1 if the thing is entering or 0 if the thing is exiting the water.