Mad Banshee in the cavern
You know the 'platform Banshee' that attacks you in the two-Wraith area prior to the underground bridge? You can quite easily lead it down the tunnel and into the cavern. Within these areas the Banshee exhibits the weird behaviour discussed in Mad Banshees (mostly in relation to level 2), namely going squash-crazy and doing grenade-chasing. Fun to play about with!
Further on, it takes on a zombie-like demeanour. When I led it over the bridge and beyond, it became zombie-like as I neared the enemies at the bottom of the rising tunnel. It just had its nose up against the wall, as if trying to move ahead regardless. Using the Warthog I was able to push it along so it was released up the tunnel. There, it continued its zombie-like behaviour all the way up, nose to the ground, occasionally needing a push to get it up over a rock. It got up into the next area but never did recover.