A technical report from the University of Michigan offers a stunningly simple theory for the source of the Cuban “sonic attack”: a pair of eavesdropping devices too close to each other and tripping the ultrasound that ironically was supposed to make their presence quiet.

More importantly, it might not have been done with malicious intent.

“It doesn’t prove it’s the cause,” Kevin Fu, an associate professor at the University of Michigan and one of the co-authors of the study, cautioned. “It’s a correlation. But to us, it seems like a strong correlation.”