Floor 9 - After Outer Sanctum

[Amerasu]

I've completed the III, II, I, III sequence of teleporters in the Outer Sanctum (on the 9th Floor) and advanced to the next little area. This little area starts on a pressure plate with two dragon heads on the left and right (moving toward either of them releases a poison cloud). Straight ahead are two collapsing tiles. When I place an item on the pressure plate, I can advance to the first collapsing tile (which is no longer collapsing). To the left of the second collapsing tile is a grate that is closed, straight ahead (past the collapsing tile), is a tile I can advance to that has a slotted metal door, to the right (of the collapsing tile) is a teleporter.

I can time the collapsing tile and the teleporter to get past the teleporter to an alcove with a lever.

However, after I pull the lever down, I can't figure out what to do next. The lever doesn't open the grate or the slotted metal door (unless it is on a very short timer). I'm not sure what the lever is doing or where to go next.

Any help would be greatly appreciated.

[Drax]

SpoilerShow

Is that a pressure plate I spy on the other side of the metal grate?

[Amerasu]

SpoilerShow

Is that a pressure plate I spy on the other side of the metal grate?

Why, yes. Yes, it is.

Thank you Drax!