If Zhen Xu hadn't annoyed her lab mates, she might never have discovered a groundbreaking treatment for liver cancer. As a PhD student in biomedical engineering at the University of Michigan in the US during the early 2000s, Xu was trying to find a way for doctors to destroy and remove diseased tissue without the need for invasive surgery. She'd landed on the idea of using high-frequency sound waves – ultrasound – to mechanically break up tissue and was testing her theory on pig hearts. Ultrasound isn't supposed to be audible to human ears, but Xu was using such a...