Bullet hole glitch
From Halopedia, the Halo wiki
In Halo: Combat Evolved, there is an odd glitch that is very easy to see/perform. Basically, shoot a BULLET (not a rocket, needle or plasma bolt) nearly perpendicular to any surface the bullet can strike and leave a bullethole (i.e. a wall, hard ground, not dirt or ice). At the point where the bullet hits, there will be a mysterious splotch of human blood.
