The scientists tested their hypothesis by replicating the "chirping" from an AP video using two ultrasonic emitters that combined tones, one at 25kHz and another at 180Hz. That produced a similar-sounding 7kHz frequency with ripples of sound at an even 180Hz spacing. The team even built a device that would simulate eavesdropping by playing a song instead of the 180Hz tone.

Don't rush to call the case closed. Researchers are quick to note that this doesn't rule out other explanations. However, it's certainly more plausible than some of the theories floating around the Cuba illnesses, such as poisoning. It's no secret that Cuba wants to know what the US and Canada are doing, but it also wouldn't gain much from inflicting nausea and headaches on embassy workers.