Mad Banshee at the underground bridge
You know the 'platform Banshee' that attacks you in the area prior to the underground bridge? You can quite easily lead it down the tunnel into the bridge area. 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. Further on, it takes on a zombie-like demeanour, as detailed in the aforementioned article.