Introduction
 Well, I made it to another Day 7  of SR!  I decided to sleep in my XO “chastity cup” overnight.  As expected, I was awakened about 4:00 AM with a strong erection.  As I began to dwell on the fact that I felt so good but was unable to masturbate or ejaculate, I became more and more frustrated.  (If there is a stronger word, I would gladly use it).    I began to think about something tangible so that I could describe the feeling.  Here is what I came up with…..
Analogy
 The analogy I discovered was that of a soda-pop bottle (like a 2-liter one).  With every passing day while in semen retention, the bottle is shaken-up a little bit more.  By Day 7, the bottle is violently shaken and all the while, pressure is building-up inside it.  The bottle actually gets quite hard from the internal pressure developed.  Anyone that has attempted to open a bottle which has been shaken-up in this way knows that a “surprise” is in store for them when they open it!  Namely, when the pressure is released, soda comes gushing-out everywhere!  
Isn’t this a good comparison to the practice of semen retention? I think so. Of course, the analogy is quite simple: The cap on the bottle is my chastity cup and my practice of semen retention. The shaking is my arousal which comes at regular intervals. An Aneros session while wearing a chastity cup would qualify as well. Removal of the cap is my removal of the cup and hence the desire and yearning and anticipation of an ejaculation. And the gushing-forth, well we all know what that represents!
Conclusion
 When in semen retention beyond Day 7, there is a strong urge to ejaculate.  It takes sheer willpower to keep that cap on the bottle!
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Source: https://www.aneros.com/blogs/the-soda-pop-analogy/