What story does this picture tell you?
Put scientifically, we learn this: The Cowper's glands, also known as bulbourethral glands, are two small (about pea-sized) structures near the base of the penis. Their function is to secrete glycerin-like mucus that lubricates and readies the urethra (i.e. neutralizing the acidity within the urethra itself) prior to ejaculation. They were named after anatomist William Cowper and are homologous to Bartholin's glands in females. Most guys know this secretion as "pre-cum". Some men secrete much more of it than others; in fact, many men don't even notice it at all.
“Many men don't even notice it at all“ – really? I guess that does not account for all you guys reading this! Precumming is indeed a very hot subject in its own right. And the fluid itself is nothing less than perfect. It is crystal clear, absolutely lubricating and bears a slightly salty taste (if any). It signals that its producer is sexually excited to his core. Hence we can read the above gif this way:
The guy is as much aroused as that he had begun to literally get wet (no difference to women here, by the way). He is nicely leaking precum from the meatus (piss-slit) of his erect cock. He may either begin to enjoy himself witnessing more precum to rise from the depths of his awakened system and watch his nectar seeping out and descending with his honey building long threads or he will utilize his produce to lube his helmet to achieve exquisite sensations while stroking his tender cockhead.
It is a fact that some guys, unfortunately, run low on precum production (causing them to probably neglect this wonderful feature of sexual response) while others leak notable amounts of this awesome stuff. This may be regarded as a genetic cause rather than contributed to some alterable parameters (unfortunately again).
Similar to the (key feature of the) seminal vesicles, the Cowper's glands constantly produce fluid when the male is sexually excited. Unlike the seminal vesicles though, the Cowper's glands don’t store their produce but secrete it continuously into the bulbous portion of the urethra where it travels immediately within the penis to surface at its tip.
This outstanding biological feat is one to enjoy in any sexual activity and may be incorporated into specific delights such as (pre-) cum-harvest and/or edging!
Some women do appreciate their guy leaking (others may not) and integrate precumming into sexplay or even love it so much that they take special focus at this striking male feature.
Finally, I need to mention very tiny urethral glands which are mainly neglected because their contribution to the overall sexual secretion is really small. I quote from Wikipedia:
The urethral or peri-urethral glands (also Littre glands after Alexis Littré, French physician and anatomist (July 21, 1658 – February 3, 1726)) are glands that branch off the wall of the urethra of male mammals. The glands secrete mucus, which is incorporated into the semen, and are most numerous in the section of the urethra that runs through the penis.
