Minecraft wiki entry for Historical_effects, associated text: When attached to a tripwire hook, the results vary visually depending on the version being played on. From 12w22a through 13w01b inclusive, it appears effectively identical to the tripwire itself. However, from 13w02a through to 1.7.10, the section attached to the hook has a very thick gray section. This is almost certaintly due to a model change that affected the brightness and shape of tripwire in that same snapshot, making that section of wire less dotty and more linear; stretching that line perpendicularly to itself would create a planar sheet, as opposed to stretching dots which would create lines.