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I was pretty sure the shutter went side to side, not top to bottom. My first guess was shutter, but then that thought popped into my mind.
The shutter on virtually all (if not all) modern cameras travels in the [shortest] direction (top to bottom). My old Olympus OM-4T has a horizontal traveling cloth shutter...VERY old school!
Same with my Pentax K1000: cloth horizontal travel.
Troy, here's an interesting (to me, anyway) video of a modern shutter in action:
It does a good job of showing how the sensor is fully exposed at 1/200 sync speed or less, but only a moving slit exposes it at 1/1000 (which is why normal flash won't work at faster-than-sync speeds.