化學課上的那張試紙
這一家就是畫面本身：真的有一張紙、一杯水、一個顏色。
noun · B2
A simple chemistry test in which a strip of litmus paper is put into a liquid to show whether it is an acid or a base. The paper changes colour, and that colour is the answer.
石蕊試紙檢驗
核心畫面
A strip of paper goes into the liquid and comes straight back out with the answer printed on it in colour. No discussion, no second opinion, nothing in between: one dip, one colour, done. English keeps that picture and hands it to people and decisions. Pick the single thing you trust to settle the matter, look at that, and treat the question as answered.
可以想成一張試紙丟進液體裡，拿出來顏色就是答案。不用討論，不用第二意見，也沒有中間地帶——沾一下，看顏色，結束。英文…更多收起
可以想成一張試紙丟進液體裡，拿出來顏色就是答案。不用討論，不用第二意見，也沒有中間地帶——沾一下，看顏色，結束。英文把這個畫面借去看人、看政策。挑出最能一翻兩瞪眼的那一項，看那一項，然後就當作有結論了。From the word’s history
The packet's Wiktionary entry gives the origin simply as 'From litmus + test': the dye that changes colour with acid or base, plus the ordinary word test. Nothing has been added to that picture; the figurative use is the same test pointed at people and choices.
證據包裡的字源只有一句：From litmus + test。litmus 是會隨酸鹼變色的染料，test 就是一般的「檢驗」。比喻的用法沒有新增任何東西，只是把同一個測試對準了人和決定。
Wiktionary entry supplied in the evidence packet (source_ref kaikki:3f6f69a190036ae4:1245607570), etymology_text: 'From litmus + test.'
Two branches
借來看人、看事的那一項判準
液體換成人或政策，試紙換成你挑出來的那一項細節。
noun · C1
One single thing that you look at in order to decide whether someone or something is acceptable, suitable or genuine. Whatever that one thing shows, you treat the question as settled.
試金石；檢驗標準