A group of FSA fighters attempting to cross a danger area in al-Qusayr don't move quick enough and find themselves on the wrong end of an enemy explosive weapon system.

There's a reason that danger areas have the word danger in them. Unfortunately, the only way to really get through a danger area is by crossing with as much speed as possible. If you fail to get through quickly, the reality of the situation usually means you, or part of your group, will end up dead. That's exactly what happens in this video, only the devastation occurs at the initial crossing point, and not in the danger area itself.

This group of FSA fighters in al-Qusayr probably had no idea they were in the sights of something that could annihilate them. I'm unsure of what weapon system we see detonating here, but it's clear to me that the group that was still waiting to cross had zero survivors.