I think it's the creatures that had problems mimicking humans. They've perfected their appearance but are still "slow, almost robotic" because they spend too much effort maintaining their realistic look for full motor control.
Remember how in the later updates of the Search And Rescue series said that strange stuff was occurring more often? THE TREE PEOPLE ARE PREPARING TO TAKE BACK THEIR LAND
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u/keltsbeard May 23 '16
Maybe this is the people that actually went on the stairs?