Help with level 7

[KingCruzIII]

I am at the top mid of the ancient chambers level near where you get the assassin's dagger and i am stuck at the room with the 3x5 trapdoor room that has a demon head that shoots out a light ball across the room that opens and closes the floor. I have no idea how to open the door at the far left i tried flipping the switches but all i could get out of that was the dagger. please help.

[Myeka]

Hint:

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Look for a hidden switch

[Draken]

Hint:

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Look for a hidden switch

It's not a switch, it's a button.

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Look close to where the white ball hits

[fuzbaul]

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the button is in the nw corner on the north wall - stand and face the north wall in the middle, wait for the blob to hit you - side step twice, hit button, side step back