system
Given the following post, respond as if you're commenting on Reddit:
human
Why do viscous liquids like honey coil when poured?

This is one science-y question for which I haven't been able to find a satisfactory answer. Most of my personal research has yielded the "nobody really knows" thing, but there have *got* to be *some* theories out there as to why this happens.
gpt
If you pour honey so that it forms a thin column from the honeypot (heh) to, say, a plate, then it will form a little coil.  The coil is formed by the interplay of two forces - inertia/motion and viscosity. Consider the path of the honey in the absence of viscosity.  That's easy -- it's the path the honey follows for most of its descent, i.e. an approximately ballistic shape, with each piece of honey falling approximately independently of the others, so that the entire stream traces the path that a single drop of honey would follow.  Now, insert a plate or something.  When it impacts the plate, the stream has to deform -- it has to go from long and thin to short and flat (part of the spreading pool).  That is a severe deformation, and the viscosity opposes it.  How?

Well, viscosity is a quantity that relates *shear motion* to *shear reaction force*.  Shear motion is a style of motion in which the velocity (a vector quantity) varies in length, if you travel perpendicular to the velocity vector.  For example, on a freeway if traffic is slow in the right-hand lane and fast in the left-hand lane, there is a leftward shear in the forward velocity of traffic.  If freeways were viscous (they have effects that act a little like viscosity, but are more complex), then there would be a reaction force decelerating traffic in the left lane and accelerating traffic in the right lane.  The reaction force would be directly proportional to the *difference* in speed between those lanes, and inversely proportional to the width of the freeway.   The constant of proportionality is the viscosity.  Ahem.

So the viscosity prevents spread of the honey as it lands, which makes a little mountain of honey.  The weight of each little drop of honey then drives deformation by squeezing the drops under it (that fell a little earlier), so the whole mound is slowly falling down and squishing out sideways.  But it turns out that, for some rates of pour, a direct-pileup mound like that is rare.  Why?  

Well, if the honey is viscous enough, it piles up a pretty high mound.  The mound is unstable to tipping over.  As it tips, the viscous forces keep the stream from disconnecting (easily), and force the next few droplets of honey off to the side.  Once they are off to the side, they pull the next few droplets and like that.  All via the viscous force.  Once the stream is going off to one side (call it a radial displacement from where it would land in the absence of viscosity) the geometry changes and it might come back to the center or move off in some chaotic path.  But for certain pouring regimes, you can get a stable orbit of the touch down spot.  In those orbits, the radial centering force imposed by the implacable fall of new droplets of honey (connected in the stream of course) is counteracted by centrifugal force as each droplet is whirled around slightly by the geometry of the existing mound of honey.  That makes the (in)famous coil.

Coiling is energetically preferred over direct mounding, since you don't have to deform the stream as much from a coil formation to get it to be flat.  In effect, a coil is already quite flat compared to direct pileup, so it doesn't take as much distortion to merge a coil with an existing puddle, as it does with a directly piled up mound.  So coil-mounds are shorter than direct mounds.  So once a coiling motion is started it's unlikely to change unless the flow from the pour changes drastically or the location of touchdown changes suddenly.