Eye-controlled focus point selection. Yes, that really did exist on some of the last of the high-spec Canon 35mm film SLRs. Once set up, you just looked at the focus point you wanted, pressed the shutter button half way (as you normally do to obtain focus) and it would lock on to the point you were looking at and focus as normal. So much easier than using a joystick, etc. and it was instant.
By the time of the last of the film SLRs, Canon had got this gadget to work almost faultlessly, as long as people learnt how to calibrate it and use it (because it tracked eye movement, looking away at the last moment before pressing the shutter half way to lock focus wasn't a good idea!). Apparently not everyone could get it to work for them (some spec-wearers for instance) and they moaned about it (despite the fact it could easily be switched off and the camera could be used absolutely normally without it).
Apparently, as it was expensive to include and had met a mixed reception (a noisy minority?), Canon didn't carry it forward to DSLRs when they started making them and this amazingly useful gadget was lost. I really wish they'd bring it back as an option on the 5D range, and I'd buy one immediately as I find it so useful when I'm using my EOS-3 and EOS 30 film cameras and really miss it when I pick up my DSLR afterwards.
Bearing in mind this gadget was 1990s technology, and they could get it to work on the 45 focus points of the EOS-3, imagine how good it might be these days? So there you go, eye-controlled focus point selection, it's probably the best gadget you've never had!