It's possible that multiple *different* ultrasonic spying devices may have interfered with one another in the recent Cuba incident! (Spy v Spy)*nonlinear => Intermodulation Distortion + Oops! This obviously violated the spooks' Hypocritic Oath: First, Do No Harmonics! https://spqr.eecs.umich.edu/papers/YanFuXu-Cuba-CSE-TR-001-18.pdf On Cuba, Diplomats, Ultrasound, and Intermodulation Distortion University of Michigan Tech Report CSE-TR-001-18 Chen Yan 1 , Kevin Fu 2 , and Wenyuan Xu 1 1 Department of Systems Science and Engineering, Zhejiang University 2 Computer Science & Engineering, University of Michigan March 1, 2018 Abstract This technical report analyzes how ultrasound could have led to the AP news recordings of metallic sounds reportedly heard by diplomats in Cuba. Beginning with screen shots of the acoustic spectral plots from the AP news, we reverse engineered ultrasonic signals that could lead to those outcomes as a result of intermodulation distortion and non-linearities of the acoustic transmission medium. We created a proof of concept eavesdropping device to exfiltrate information by AM modulation over an inaudible ultrasonic carrier. When a second inaudible ultrasonic source interfered with the primary inaudible ultrasonic source, intermodu- lation distortion created audible byproducts that share spectral characteristics with audio from the AP news. Our conclusion is that if ultrasound played a role in harming diplomats in Cuba, then a plausible cause is intermodulation distortion between ultrasonic signals that unintention- ally synthesize audible tones. In other words, acoustic interference without malicious intent to cause harm could have led to the audible sensations in Cuba.