So this has happened more than once now, twice actually. This is the second time that I've come back to this: That's right. There's a living, breathing, floating arm in the top left. It stays there and copies my arm's movements. I think it's after me. Has anyone else experienced this?
There's 2 instances in which this will occur. 1: Random Graphical Glitch that I've no idea what could cause it for (Your case) 2: You threw a harpoon and quickly switched to another weapon, which makes the gun all fubar'd looking.
The "Random Graphical Glitch" that Euphanic descrbies usually happens due to lag. Trust me, I would know due to the randomm lag spikes I get from 60-80 ping to 700-800 ping. It also happens with the harpoon thing and it's just random.