Possibly the most difficult problem of all that bats face is the danger of inadvertent 'jamming' by the cries of other bats. Human experimenters have found it surprisingly difficult to put bats off their stride by playing loud artificial ultrasound at them. ... Many species of bats roost in enormous aggregations, in caves that must be a deafening babel of ultrasound and echos, yet the bats can still fly rapidly about the cave, avoiding the walls and each other in total darkness. How does a bat keep track of of its own echoes, and avoid being misled by others? ... [E]ach bat might have its own private frequency, just like separate radio stations. To some extent this may happen, but it is by no means the whole story. ... It seems that bats may be using something that we could call 'strangeness filter'. ... The bat's brain relies upon the the assumption that the world portrayed by any one echo pulse will be either the same as the world portrayed by the previous pulses, or only slightly different.

[The American zoologist] Donald Griffin tells a story of what happened when he and his colleague Robert Galambos first reported to an astonished conference of zoologists in 1940 their new discovery of the facts of bat echolocation. One distinguished scientist was so indignantly incredulous that

he seized Galambos by the shoulders and shook him while complaining that we could not have possibly mean such an outrageous suggestion. Radar and sonar were still higgly classified developments in military technology, and the notion that bats might do anything even remotely analogous to the latest triumphs of electronic engineering struck most people as not only implausible but emotionally repugnant.