Ultrasonic sound

1.         Ultrasonic sound is the sound which help animals to 👀 detect their enemies from long distance. In our surrounding we know about this animals but we don't observed them like 🦇Bat,🐈 Cat, 🦮Dogs, etc.
   
2.        Sometimes they hear, sound around their which are not able to hear by us means by humans or specially mammals because we have heard sound from 20 Hz to 20000 Hz.   
3.             That's why we ignore their activities and one thing is that the human child means the👶 baby child have age less than 5 years also hear such kind of sound because of the capacity less than 20 Hz and we think that time the baby smiles just because of seeing our activities.