Is this the type you saw, WA? A fellow named anzac16 posted a pic of his over at a WW1 forum, and he describes it as working basically the same way as a standard pair of garden shears. The soldier would push the rifle into the wire, and the body of the cutter is hinged so that as it rotates backwards, the two cutter blades (riveted onto the body of the cutter with those two largest rivets) cam together, cutting the wire.