jhāna constipation understood by analogy and example

Well, not exactly analogies. Since wave interference patterns happen with physical particles, electromagnetic waves, and bio electric qi flowing through energy meridians in a jhāna meditator, it's more than an analogy. Here are some examples:

1. Water bottle necked

With the bottle on the left, the volume of the water trying to exit the bottle neck, is greater than the volume of the small bottle neck. The excess water volume bounces back, and thus the water drains slowly. With the the bottle on the right, he shakes it so it forms a tornado of spiraling water flow, so the volume of the water trying to exit matches the volume of the bottleneck a lot more closely, so you don't get much water bouncing back and it makes a much quicker exit.

Now imagine the two bottles are jhana meditators. The one on the left, would experience bodily shaking or trembling. The one on the right, would feel vibrations in his body, but not shaking. Now if continues to practice meditation correctly, over time the bottleneck would increase in size, and the the vibrations would decrease.

2.  Toilets that flush properly

Most toilets are horribly designed. They don't flush properly, and it's easy to clog. At one time, when I used to eat almond butter regularly, it had an unfortunate side effect of making my feces rubbery and powerful. I must have clogged hundreds of toilets that required plunger emergency assistance, and required thousands of double flushes to flush my waste. For my own home, I fixed the problem by getting a properly designed toilet. The key point is, the shape of the waterway is such that when the toilet is flushed, the water goes down in a smooth path, with no place to rebound. Similar to example 1 above with the bottle neck problem. 

Always a good opportunity to do some asubha:

3. electromagnetic coils

Electric motors that spin, do so by means of electromagnets. Remember electromagnetic physics and the right hand rule? If you have a coil of wires wrapped up neatly in circular layers, it induces an magnetic wave perpendicular to it. Recently, my vitamix blender started to choke on the slow speeds. It sounded and felt like meditators with jhana constipation. This is due to the coils of wires getting old and melting together from the high heat appliances, and the waves are no longer being issued smoothly and working in sync. Some of the rogue waves start cancelling each other, like the toilet that won't flush properly from #2, and the bottleneck from #1. So the blender loses power, starts churning and groaning, shaking and tremlbing and not delivering smooth and even power. 

Similarly, a jhana meditator who doesn't keep up his meditation and physical health, his energy channels will start to decay and cause him to choke, sputter, tremble, vibrate and shake.