Flow-based echolocation of silent prey

We propose a theory for sensing a motionless particle suspended in a fluid. The principle is analogous to active sonar except with flow instead of sound; it relies on generating flow and detecting minor distortions induced by the particle. A simple analytical model shows that the size and location of the particle can be sensed remotely using pressure or hair sensors. This informs how some organisms, e.g. blind cavefish and copepods, may be able to actively hunt for prey without light or sound.