You know...
I was struggling for an adequate analogy. I first thought of sap on trees, but then started thinking of the phrase "slow as molasses in winter". I didn't think progress moved quite that slow so I compromised and came up with molasses running down trees in spring - never mind imagining how in hell it got there!
I knew as I clicked post that it was an awful & awfully messed up analogy. I apologize.
When messing with analogy it's almost impossible not to make an ass of oneself.
;-)