Picture the small turn your stomach makes before you have decided anything: the needle comes out, and you are already looking at the ceiling. Squeamish is that turn, and the person it happens to. Later the same turn can happen with no blood in sight, when the thing you are asked to do feels wrong to touch.
From the word’s history
Wiktionary calls the origin obscure, and suggests a merger of squeamous, from Middle English squaimous and Anglo-Norman escoimus of unknown origin, with dialectal sweamish, from sweam, a sudden qualm of sickness.
Wiktionary 說這個字的來源不確定，可能是兩條線合起來的：一條是 squeamous（經中古英語 squaimous、盎格魯諾曼語 escoimus，來源不明），另一條是方言的 sweamish，來自 sweam「一陣暈眩或噁心」。後面這條剛好對上核心畫面裡那突然翻上來的一下。
Wiktionary entry for squeamish, packet source_ref kaikki:3f6f69a190036ae4:926856050
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