So here we were in the SB Nation New York office watching Serena Williams and Sloane Stephens play in the French Open when something dropped all our jaws. Some other people on the Internet caught it, too:

Can someone explain to me why the plane shadow is going backwards??? #FrenchOpen pic.twitter.com/skYtg9YfrN — Zeb Goodman (@ZebG1996) June 1, 2015

You see it, right? The shadow of a plane zooms across the court ... BACKWARD? WHY IS THE PLANE FLYING BACKWARD? WHAT THE HELL IS GOING IN FRANCE? A lot of people wondered about this, and it wasn't just during the Stephens-Williams match:

Why was the shadow of the plane going backwards at the French open? It's weirding me out!? Anyone else see it? — Sam Williams (@Williams_297) June 1, 2015

Did anybody just see the backwards flying plane at the tennis?! Wtf #FrenchOpen pic.twitter.com/sMtjeSVWQd — th@und@d@wg ™ (@thaundadawg) May 25, 2015

So why was that plane flying backwards though lmao everybody had to see that #FrenchOpen — william jones (@the3hrill) June 1, 2015

A plane's shadow just moved in reverse across the court in the @rogerfederer vs @Gael_Monfils match at the #FrenchOpen... #gohomeplanedrunk — Ananthapadmanabhan R (@ananth_r) June 1, 2015

There are videos of this phenomenon going back a couple years:

So what is it? Are French pilots huge show-offs? Is the shadow somehow reflecting off something? Is that possible? Is it a UFO? IS IT CHEMTRAILS!?

Nope, it's an ad.

(Julian Finney, Getty Images)

The wire camera at Roland Garros, which spans the width of the court, has a model plane affixed to it as an Emirates Airlines advertisement. When it slides forward and the sun is overhead, the shadow of the plane goes forward. When the camera slides backward, the shadow of the plane goes backward. It's not flying. It's not a mystery. It's just brands. Nothing is ever fun or exciting. The Loch Ness monster is probably viral marketing.