It is one of Google’s most famous "Easter eggs," a hidden feature programmed into the browser as a nod to the Nintendo game Star Fox 64 (where the character Peppy Hare instructs you to do the maneuver).
If you want to see it in action, click here or go to Google and type it in yourself. do barell roll
Do not attempt this maneuver in a real aircraft without proper training, certified aerobatic aircraft, and altitude clearance (minimum 3,000 feet AGL recommended). This guide is for flight simulators or theoretical understanding. It is one of Google’s most famous "Easter