空氣中瀰漫著刺鼻的火藥味，你手裡握著一把還帶著餘溫的武器——剛剛發生了什麼，幾乎無從否認。正因為這幅畫面太鮮明，「冒煙的槍」（a smoking gun）才會讓人覺得格外有說服力。
一般認為，這個說法源自字面意象：如果有人被當場逮到手裡拿著一把還在冒煙的槍，那對他極為不利，因為這暗示他可能在片刻之前才剛開過槍。
如今，「冒煙的槍」指的是能一錘定音、足以定案的確鑿證據，尤其是能證明不當行為或責任歸屬的證據。它常見於新聞、政治、法律與日常對話，用來形容那種很難搪塞、很難辯解的證據。
應用
• 使用頻率：8/10
• 適用場合：Casual, Professional
例句
• The security camera footage of her walking out with the laptop was the smoking gun that proved she stole it.
(監視器拍到她拿著筆電走出去，那就是她偷筆電的鐵證。)
• We’ve been trying to figure out why the system crashed for weeks, and this log file, showing a critical error right before it happened, is definitely the smoking gun.
(我們找系統當機的原因找了好幾個禮拜，而這個紀錄檔，顯示當機前有個關鍵錯誤，這根本就是鐵證啊！)
• The deleted emails were the smoking gun that proved the CEO had been hiding the company’s financial losses all along.
(那些被刪除的電子郵件就是鐵證，證明執行長一直在隱瞞公司的財務虧損。)
