Normally, ticks flitter about in the air, seemingly oblivious to the player. Usually nonaggressive, they serve only to obstruct the player's path, and to slightly clutter the motion sensor. On higher difficulty levels, however, the ticks will explode in a fiery cloud when destroyed.
- Several different types of ticks were originally conceived for Marathon 2, including the Energy Tick and Oxygen Tick. For the final release, however, the ticks neither attack, nor do they appear to adversely affect the player's health or oxygen levels.