Tracers work both ways. The only thing more accurate than incoming enemy fire is incoming friendly fire. If you take more than your fair share of objectives, you will have more than your fair share to take. Both sides are convinced they are about to loose. Both sides are right.
Professionals are predictable, but the world is full of amateurs.
Murphy was a grunt. A magazine contains x-number of bullets. The basic mentality for this is that if someone is out there where they don't belong, they deserve to get hit. A claymore is an anti-personnel mine filled with things like shotgun shot, small sharp pieces of metal, etc. It is connected to the detonator by wires, and fired by a small switch.