One thing that did bug me a bit....why wasn't the gravity going all wonky on the ice level as well?
Maybe there's a degree of insulation between layers. The music became more muffled the farther down they were.
^ They were just a representation of the actual dream initiation boxes, just as the weapons were. Think of them as physical representation of a mental trigger. The characters weren't actually hitting the button and sending chemicals. Hitting the button representation caused the characters to believe they were initiating a second or third dream within the main dream. The mental safes or vaults would work in the same way. But this is really all part of Nolan's ideas on reality that he was exploring. What is real? What is just a representation? Is reality just an idea that has subjugated us?
That sort of makes it the opposite of existentialism, doesn't it? Consider the scene at the beginning of the last episode of Firefly, when River picks up what she sees as a bent stick, but is actually a gun. The idea being that function and purpose is an illusion, and the object only exists in and of itself. It's a hunk of metal. It could be used to propel smaller hunks of metal through people, or it could be used to prop up a wobbly table or as food for rust or simply appreciated for its aesthetic properties.
In the dream, though, the object is all function and purpose. If a non-expert cracked open the dreamed dream box, it would probably just be empty, or a nonsense mass of generic wires and parts that couldn't work. It does, though, because the important thing is the idea
of the dream box, of how you expect it and believe in it to work. Going deeper into another level of dream could've just as easily been represented by walking through a magic door or taking an elevator between floors.