Running and disturbance.

The general rule is: whatever is behind you (and so ignored previously), determines what you ignore moving forward. This is calcaulated separately for the tiles to the left, to the right and in the middle along the running direction. So, if you want to ignore something start running when you stand on it (or to the right or left, respectively) or by entering it (or passing to the right or left, respectively).

Some things are never ignored, such as: enemies seen, imporant messages heard, solid tiles and actors in the way.