Erratic proximity polling by a mobile Mine
From Worms Knowledge Base
When a Mine checks for nearby worms to see if it should arm itself, it does not check every frame (1/50th of a second) as this is unnecessary and would cause extra calculations per second for the game. Instead, it only checks for them every 1/5th of a second. In most circumstances, this does not cause any problems. However, when a mine has been moved by a particularly large explosion, or dropped from a large height, such as when you use a Mine Strike, it can gain quite a high speed. This high speed will allow it to move quite a large number of pixels in a few frames. This means that it is entirely possible for a fast moving mine to move past a worm without setting it off.
A similar situation can also occur if a mine is stationary, but a worm on a Ninja Rope is moving at maximum speed and swings close to the mine. The worm moves fast enough to completely pass through the mine's detection range during the frames that it is not checking for nearby worms.
Of course, this trick requires a large amount of luck to sucessfully work. It will only work if the mine is near the worm during the frames that the mine is not checking for nearby worms, which is nearly impossible to judge.
