If a Random Walk zombie does not smell the player, then, on each decision step, the zombie will choose, with uniformly distributed probability, a heading 0.0 through 360.0 degrees from east.
After choosing a heading, the zombie will continue to move in that heading until the next decision update.
When a zombie collides with a wall or obstacle, the collision detection must stop the zombie at the wall. However, the zombie will continue to attempt to walk in that same direction until its next decision update.
On a decision update, if a Random Walk zombie had on the previous update hit a wall, then the zombie will not choose to move in that same direction.
On a decision update, it a Random Walk zombie is adjacent to a wall, but did not hit that wall on the previous update, then the zombie will not favor nor disfavor that direction.