If you heard your friends talking about Love Balls recently, they weren’t talking about props from Fifty Shades of Grey.

Instead, Love Balls is a smartphone puzzle game that has taken players around the globe by storm since it was released four months ago.

Love Balls is all about uniting those two balls.

App Annie data shows that last month it ranked number one among free iOS apps in North America for almost two weeks straight -- and also topped the charts in Australia, France, Germany, Sweden, Switzerland and the UK.

The game is simple: Players have to make two balls collide with each other by drawing all sorts of contraptions. These can be as straightforward as a slope, but that won’t cut it when you jump to harder levels. Each round can be completed as quickly as a few seconds -- one reason why it’s extremely addictive.

Two balls, in love with each other, reunited by physics.

But where did the game come from?

Love Balls is developed by Supertapx. Little is known about the secretive company, whose apparent website doesn’t seem to show anything other than legal disclaimers. Its terms of use cite Israeli laws, while Love Balls’ Google Play page shows a British Virgin Islands address.

Many though believe Supertapx is actually from China. A new report from US research firm Sensor Tower lists Love Balls as the world’s most downloaded Chinese mobile game last month, ahead of Tencent’s PUBG Mobile.

Some industry observers in China, citing sources close to Supertapx, suspect it’s a Chinese studio operating under AppLovin -- a California-based mobile marketing company that received a massive Chinese investment last year. It does seem like creating a low-cost viral game could be a viable way to spread ads.

We tried to contact Supertapx through email and Facebook but did not get any response.

Besides Love Balls, another Supertapx puzzle game also made Sensor Tower’s top ten. Ranked number seven, Draw In was only released in recent weeks but already attracted more downloads in May than established titles like Tencent’s Honor of Kings and NetEase’s Rules of Survival.

Other names on that list include: Mobile Legends: Bang Bang, Lords Mobile, Piano Tiles, West Gunfighter... and a game called Shoot Hunter-Gun Killer (seriously).