Hands! Most people have one or two. But in a virtual reality game, you typically don't have any; right now, most VR game makers are making due with rough approximations or just foregoing hand-rendering entirely.
But the presence of believable hands in first-person VR games goes a long way towards immersing players in the experience; it's so critical, in fact, that around this time last year Oculus was talking up hand controllers and "hand presence" as the future of VR games.
Dutch startup Manus VR has taken that concept and run with it, prototyping a VR glove controller prototype in 2014 that it's currently preparing for a commercial release. Yesterday the company published a video showcasing what it looks like to use its prototype glove controller with the HTC Vive, and it's well worth watching for VR devs.