h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

If "'Ultrasonic' means that the frequencies used are beyond reach for human ears" why do the bats round my house drive me absolutely crazy with their noises...?! It goes right through me and makes me want to curl up in a ball on the floor screaming and holding my ears!!!!!! Aaaarrrrrggghhhhh!!!!!!! Aimi x

most likely because you can hear somewhat higher frequencies than the 'average' human - which is not surprising in that none of us are carbon copies. I know I can hear the ultrasonic cat scarers my parents use - but they can't.

Equally, bat frequencies are an average two - maybe some of your bats have a very slightly lower frequency.

As you grow older and your hearing fades a bit you'll probably find that you stop hearing them at some point.

Echolation is an ability humans can develop as well and is often reported with the blind, with a difference, instead of being able to resolve images in the ultrasonic of objects smaller than a millimeter, normal human hearing allows resolution down to only about 7.5 cm.

The theme was used as basis for one of the 1960s "Hawaii 50" episodes in which Jack Lord was supposed to have temporarily lost his sight.

As a matter of fact when people develop the ability as a consequence of temporary blindness and afterward regain their sight, the ability tends to stay with them.