Your article didn’t specify how strong the ultrasonic waves were or if any special conditions were required for these bubbles to form. I am curious to know if there’s a difference between the ultrasonic waves mentioned in your article and those in ultrasound exams of pregnant women.

Andrea Bikfalvy
Dowagiac, Mich.

The article made me wonder whether the ultrasonic waves of naval sonar can “rattle” an aquatic mammal’s brain. If so, it bears some serious investigation.

Debbie Butler
Vashon, Wash.

The shorter duration and higher frequency of diagnostic ultrasound make bubble formation less likely than with the ultrasound used in sonoluminescence experiments. As for marine mammals, some investigators suspect that bubbles may form in blood and tissues exposed to sonar and that the result can be animals stranded on beaches. Deep-diving marine mammals may be particularly vulnerable to ultrasonic-bubble formation because they have large amounts of dissolved gas in their bodies. —P. Weiss