Sound is something that you hear through your ears. It is made up of vibrations that can travel through air as well as many other substances. Sound won't travel through everything - many substances block sound.
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A squeak is a short, high-pitched noise. Small animals like mice squeak. Metal surfaces that are not well lubricated will squeak when they rub together, for example a squeaky door.
Thunder is the loud rumbling sound made by lightning. Thunder can also describe other loud noises, for example "the herd of horses thundered by".
A toot is the sound a horn makes, or anything that sounds similar to that noise.
A tweet is a short, high-pitched noise made by small birds and some baby birds. Another word for tweet is chirp.
A whir is a humming or buzzing sound made by something quickly moving backwards and forwards or around and around. Things that whir include electric fans and bird's wings.