Babies crying on an airplane never sounded so good.

Passengers on a recent JetBlue (JBLU) flight were awarded a free round-trip flight thanks to four crying baby travelers.

"People smile at babies everywhere, except on planes," said Elizabeth Windram, JetBlue's director brand management and advertising (and a mother of a toddler). "For Mother's Day, we wanted to acknowledge how moms (indeed all parents and caregivers) often feel stressed while traveling with children."

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The airline offered the "FlyBabies" promotion on April 15 on a flight from New York City's JFK airport to Long Beach, California, that awarded a 25% discount on future airfare every time a baby onboard cried.

There were a total of five babies on the flight.

All it took were four cries (fussing and whining didn't count) for the 140 passengers to be rewarded with a free roundtrip ticket on JetBlue.

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With a flight time of around seven hours, there was a good chance the pint-sized travelers were going to get fussy.

Passengers were made aware of the stunt after the first food and beverage service -- and the four cries came before the plane made its final descent.

Despite the fact that crying babies meant future discounts, passengers were helpful to the parents, according to JetBlue spokesperson Morgan Johnston.

"We weren't necessarily sure what to expect from folks on board, it was interesting to watch. We started seeing people really want to entertain the kids and make it a comfortable environment on board."

The airline said the goal of "FlyBabies" was to address a topic that people tend to shy away from.

"We've had this ongoing mission to inspire some humanity, and we thought this was something we cold weigh in on," said Johnston.

It also documented the flight and has posted the video online.