One way to hold this word: a thin, high sound that gets pushed out and held for a moment. A lifted off the ground makes it. So does a child who has just won a prize, and so does a tyre dragging on wet road. The sound is not chosen and not planned — something happens, and the noise comes straight out.
Wiktionary traces the word to Middle English squelen, probably from Old Norse skvala 'to squeal, bawl', and further back to a root meaning 'to ring, resound, cry'. It also points to Swedish skvallra, 'to babble, chatter, tell on' — so the step from making a noise to giving someone away is already visible in the word's relatives.
來源字典把這個字接到中古英文 squelen，可能來自古北歐語 skvala（尖叫、大聲喊），更早的字根意思是「響、鳴、喊」。同一則資料還指出瑞典語的親戚字 skvallra，意思是「閒聊、把人講出去」。所以從「發出聲音」到「把人供出去」這一步，在這個字的家族裡本來就看得到。
Wiktionary 'squeal' etymology in the supplied packet (kaikki:3f6f69a190036ae4), including the cognate note 'Swedish skvallra (to babble, chatter, tell on)'.
Two branches
那個又高又細的聲音
這一組就是核心畫面本身，只是分成「誰在叫」和「那一聲」兩種說法。發聲的可以是人、動物，也可以是摩擦中的機器。
verb · B2
To make a long, loud, high sound — with your voice, as a person or animal does, or as a machine, a tyre or a brake does when it rubs against something. You can also squeal words, saying them in that high sound.
尖叫；發出尖銳聲
一叫就把人暴露了
聲音一旦跑出來，藏著的事情就藏不住了。這一層把重點從「聲音好不好聽」換成「因為出聲，別人知道了」。這是教學上的連結，同時也有語源上的旁證：同源的瑞典語 skvallra 就是「把人講出去」。
verb · B2
To tell the police, or someone else in charge, about something wrong that a person you know has done. It is informal, and it treats the telling as a betrayal of your own side.
告密