Totems
The world of Inception is populated by small objects called totems, carried around by dream-sharers to let them know definitively they are not dreaming. Totems are unique, hand-crafted objects that hold a special significance for their owners, such as Ariadne's golden bishop, or Mal's spinning top. The fact that Cobb uses Mal's totem reflects the fact that he has not been able to overcome the power of her memory.
Elevators
Christopher Nolan uses the image of the elevator to depict the "levels" of the dreaming mind, with the subterranean levels symbolizing the most repressed content. When Ariadne descends in an elevator into Cobb's subconscious, she sees him with Mal in their anniversary suite—memories that Cobb cannot relinquish.
Paradoxical architecture
Arthur and Cobb both show Ariadne how impossible objects are possible in dreams. For instance, Ariadne bends the laws of physics by folding city streets back on themselves, and Arthur shows her how a Penrose staircase (a set of stairs that connects but seems to only go up) is an impossible object that can be realized in a dream.
Extreme slow-motion
In order to show how different layers of dreams are unfolding at different speeds, Christopher Nolan uses extreme slow-motion when cross-cutting between different planes of action. Scenes like Cobb falling into the bathtub and Yusuf plunging the van into the water both transpire at excruciatingly slow rates, which conveys how time is distorted when the team is submerged in secondary and tertiary layers of dream-worlds.
Zero gravity environments
When Yusuf drives the team's van off a bridge in the first layer of Robert's dream, the state of free-fall causes the second layer of the dream to become weightless. Arthur must improvise a way to simulate a "kick" despite the zero gravity environment, which he does by rigging an elevator shaft. When Cobb introduces Ariadne to dream-sharing, she walks up walls, showing how the physical laws of gravity in dream-worlds can be manipulated.
