身體上一碰就有反應
這一組是字面上的用法：被碰的是身體，反應是笑或想咳。核心畫面幾乎原封不動地留著。
adjective · B1
A ticklish person laughs, jumps or pulls away when you touch a soft part of their body lightly, such as their feet, their sides, or under their arms.
怕癢的
核心畫面
Think of a fingertip moving towards a soft spot — the side of the ribs, the sole of a foot. Nothing has happened yet, and the body is already reacting: a laugh, a jump, a pulling-away. That is the whole picture inside ticklish. The touch is light, the spot is the kind that answers back, and the answer is immediate and out of the person's control. Every use of the word keeps those three things: light contact, a place that is easily set off, and a reaction you cannot stop.
可以想成有一根手指慢慢靠近你最敏感的地方——肋骨旁邊、腳底心。其實還沒真的碰到，身體就已經先反應了：笑出來、縮起來、…更多收起
可以想成有一根手指慢慢靠近你最敏感的地方——肋骨旁邊、腳底心。其實還沒真的碰到，身體就已經先反應了：笑出來、縮起來、往旁邊躲。ticklish 的整個畫面就在這裡。碰得很輕，地方剛好是會有反應的那一種，而那個反應是自己擋不住的。這個字的每一個用法，都還留著這三件事：輕輕一碰、一個一碰就有反應的位置、還有停不下來的反應。From the word’s history
Wiktionary derives ticklish from the verb tickle plus the ending -ish, which often means 'having that quality, easily like that'. So the word starts out meaning literally 'easily tickled', which is exactly the picture above.
依 Wiktionary 的說明，ticklish 由動詞 tickle（搔癢）加上字尾 -ish 組成，-ish 常表示「帶有那種性質、容易那樣」。所以這個字一開始的字面意思就是「容易被搔到癢的」，正好就是上面那個畫面。至於後來用在事情上的「棘手」，是一種好記的延伸想法，這裡不當成歷史演變的主張。
Wiktionary entry for ticklish, etymology_text in this packet (kaikki:3f6f69a190036ae4:870881072:17476)
Two branches
場合上一碰就出事
把核心畫面從身體搬到事情上：這種場合也是「輕輕一碰就有反應」，所以手要放輕。
adjective · B2
A ticklish problem, question or situation is hard to handle and has to be dealt with carefully, especially because one wrong word could upset the people involved.
棘手的