Barbed Wire
From WikiRaider
Barbed Wire is a trap often used in Tomb Raider III. It can be found on top of fences, buildings and on ground. If Lara is caught in this, runs through it or jumps into it, she will be killed. In order to get round being killed while moving through it, walk instead.
Barbed wire is also used in several custom levels, there however it is often not safe to walk through.