It’s a centipede!!!
Specifically: a highly evolved giant centipede from the grasslands of a low gravity, oxygen rich world. The legs are clustered together, and are long and spindly both to aid in locomotion and also to help entangle (or ‘brush up’) potential prey. The high center of gravity of this creature is actually of help to it, as in the low gravity it means it can lean further forward and use it’s many bafflingly interlaced legs to move across the ground both at high speed and very efficiently, much like humans use their height and balance to run very efficiently for their speed.
The rear segment has developed and elongated, and the centipede holds itself vertically (head down) to use its rear segment as a nice, large acoustic surface for identifying potential prey (the local mouse population seems particularly hapless). They can also stridulate (Make noise by rubbing together) stiff hairs on this section, producing high frequency sounds that allow them to effectively echolocate.
When prey is identified the centipede will scuttle towards it, confuse and entangle it in the many legs, bite it several times (poison may cause hallucinations such as pink elephant ballet etc), then hunker down to enjoy its meal. If the prey escapes the centipede will simply not stop chasing it, never pausing or ceasing in its pursuit of its goal.
If a rival predator should appear the centipede has one further trick up it’s sleeve. The legs of the back section have become remarkably stout, enabling it to grasp its prize and temporarily elevate it out of reach of it’s competitor. This behaviour has led to taller, thicker bodied centipedes outcompeting their neighbours, hence the ‘brush like’ appearance and the prominent arms.
The wood like texture and synchronised swaying are both camouflage. Juveniles in the long grass must look grasslike, so they sway to the sounds of nearby grass movements. more adult centipedes must look inedible, so their hide takes on a more sticklike demeanour to confuse predators.
Now: groups of these centipedes (plural noun: cupboard) will naturally synchronise with each other, swaying in time to pretty much any rhythmic, often repeated noise. If they hear something moving that is out of time they will swarm it in order to ascertain if it is food, then engage in lifting and wrestling the prey from each other while taking opportunistic bites.
Oh, and in response to periodic flooding of the plains: They’re amphibious too.