In Fallout New Vegas I went to Vault 34 (If I remember correctly) and I was picking off Gold Geckos with my hunting rifle, when I ran out of ammo and the last one was still running at me, I took out my revolver, it hit me and did 3/4 of my hp in one hit (Due to fail armor), I ran out of stimpaks (I just realized this) and I had a single chance to shoot this gecko or I die, so I went into VATS aimed for the head and missed, BUT I hit it's foot(crippled) which stopped it for a second, long enough for me to take a second shot and kill it.