When you disposed of the inhabitants of this room, shoot the bloody grate. Small gift for you there.

Just round the corner from secret #1 (you see it at the back right) is a small lift. Make the lift rise, then jump into the hole under it. At this point, you may well need the item in here...

Get past the row of shooters. As you leave them behind, look up and to the left. There is a red "Q" button in the celing. Shoot it, and a (occupied) room with goodies opens.

Jump to the top of the cage. The door over it will open as you land. Grab the goodies, but be careful if you jump down at the end of the corridor - you will land in front of the shooters! Better see if you can slip back out on the top of the cage again.

Before you jump to the top of the cage, you'll probably want to dispose of the little, annoying and angry fellow inside it.
When you've done that, the door to the left of the cage opens. It's already open in #4. Feel free to peep inside.


Thanks to Mauritorami for reminding me about this one... :)