As for the slithery noise, I am pretty sure that one of the tripod legs of my camera must have slipped a few inches: if it did so, it may easily have jolted the lens cap off the baseboard, which would account for that queer little tap which I heard directly after.

He bought an Olympus camera that had a sliding lens cover and would fit in a pocket.

periscopic lens^; telescope, glass, lorgnette; spyglass, opera glass, binocular, binoculars, field glass; burning glass, convex lens, concave lens, convexo-concave lens^, coated lens, multiple lens, compound lens, lens system, telephoto lens, wide-angle lens, fish-eye lens, zoom lens; optical bench.

For the 3 1/4 x 4 1/4: One lens 4 or 4 1/2 focus One lens 6 or 7 focus One lens telephoto or telecentric 9 to 12 focus The camera should be made of metal and fitted with focal-plane shutter and direct view-finder.