technically, if the tanks were dead straight and the angle of viewing was dead straight, both pieces of glass would be see-through. as soon as there's an angle, it wouldn't be so easy. i think. it might also make a difference what the angle of light is, but i'm not sure on that one.
50gal planted - yoyo loaches, BNs, odessa barbs, giant danios
33gal planted - praecox rainbows, gold ram, bolivian rams, sparkling gouramis, licorice gouramis, lots of shrimp
2 x 5gal planted - bettas