Tiny, mouse-like bird of tepui forest understory. Entirely dark rufous-brown with a stubby tail. Found only in humid, mossy forest on tepui slopes, mostly above 1000 meters, where it is difficult to see, staying close to the ground as it crawls over roots, rocks, and large branches. Usually encountered alone and does not follow mixed-species flocks. Most easily detected by its extraordinary song: a variable series of short, pure whistles, rising and falling but usually ending with several notes on the same pitch; humanlike and easily imitated. May pop into view in response to imitation or playback, bobbing nervously before disappearing. Could be confused with Tepui Wren, but is darker brown overall and lacks buffy eyebrow.