Japanese Yakuza used to implant glass ‘pearls’ in their penis for every year they served in prison

Members of the Japanese organised crime syndicate the Yakuza have been known to count their years in prison using glass 'pearls' implanted into their penises.

Because who needs calendars?

There's nothing like a bit of body modification to mark an occasion, and while the practise of 'penile pearling' appears to date back to at least the 1400s, a report from the Journal of Urology shows it's still going on in some capacity today.

Origins of the tradition trace back to East Asia, with an early form of the practise, said to have been prominent in the Philippines, described by historian William Henry Scott.

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According to Scott, Filipino males initially had the bar implanted through the head of the penis, before adding beads and decorations to it over the years as they aged.

The additions to the piercing were designed to enhance sexual pleasure of the men's partners, but over time the tradition has evolved and is more commonly seen now as subdermal penile implants - the kind that can be placed under the skin, typically in the form of small, round implants as the 'pearls'.

Over time, the tradition was picked up by a subgroup of Filipino sailors as well as Japanese Yakuza members.

The Yakuza has existed for hundreds of years and can be traced back to as early as 1612, according to the US Department of Justice.

Gang members control businesses and act as loan sharks, as well as dealing in drugs, money lending and porn.

Naturally some of these acts can result in prison time, and the Journal of Urology explains that the Yakuza are believed to have added a pearl to their penis for each year spent in prison.

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The practise is thought to have spread to other communities as a large Australian study revealed 5.8 percent of participating prisoners had a subdermal penile implant, 73 percent of which were implanted while in prison.

Without easy access to the materials needed to conduct a professional subdermal penile implant, prisoners are described as having used random items including toothbrushes, dominos, melted plastic caps and deodorant roller balls to fashion the pearls before having them inserted into their bodies.

The journal advises urologists today to 'be aware of potential complications from this procedure primarily in the form of infection, whether that be local or blood borne'.

So there you have it. Everything you never knew you needed to know about penile pearling.