MGS1 Pal Key - The Rat

The rat sucks. If you're going for Big Boss rank, you're going to have less than 11 alerts after losing the PAL Key, which means it'll be in a rat instead of the drainage ditch.

The first thing to understand is that the rat has one fairly simple circular route that it loops through. This route has the following steps:

1. Hang out in the south area near the drainage ditch (vulnerable) for an extended period
2. Enter the vent system and go directly to the right side of the ditch
3. Exit the vent and swim through the ditch (vulnerable) to the separate vent at its top right
4. Run through the new vent for a while, turn around and come back to the same opening
5. Swim back through the ditch (vulnerable) as in step 3, but in reverse, and back into the main vent system
6. Take the vent all the way to the north-west area, doubling back unnecessarily a few times
7. Exit at the north-west and hang out there (vulnerable) for an extended period
8. Reenter the vent and return (with less doubling back) to the south area near the ditch

This route is laid out through a set of 92 waypoints (about 20 at the ditch, about 30 in the north-west, and about 40 elsewhere), which are the key to the rat's random positioning.

When the area is about to begin, the same random function explained in the ditch article is used to select a random number between 0 and 91. The rat is then placed at the waypoint at that index, and set to move along its route starting from that waypoint. This means that effectively there are 92 variations on rat behaviour, even though they're just different start points on the same single route.

If the rat is alerted by you, it will immediately run to the next vent on its route, and then continue from there. There may be some other unidentified random behaviour that I'm not aware of.