Minecraft 1.4.7, Snapshot 13w05b, Minecraft 1.5, Snapshot 13w11a, Minecraft 1.7.4, Minecraft 14w05b, Minecraft 14w06b, Minecraft 14w07a, Minecraft 14w08a, Minecraft 1.7.5
Minecraft Version: *13w05b* (tested on snapshot and 1.4.7)
Operating System: *Windows 7* (amd64) version 6.1
Java Version: *1.7.0_10*
Build floating tripwire connected to a hook.
Look from the top and the bottom at the block with the hook.
From the bottom the tripwire doesn't look like connected, it's invisible.
Hope my english is not too bad