病本身會傳、人身上帶著會傳的病
這是核心畫面的字面用法：真的會跨過空氣、跳到下一個人身上的疾病，以及正帶著這種病的人。
spreads person to person · adjective · C2
An infectious illness can pass from one person to another, especially through the air you breathe.
傳染的
核心畫面
One way to picture it: something that does not stay inside one body — it crosses the air between people and takes hold in the next person. The key is not that it is bad, but that it moves from person to person on its own.
比較像：某個東西不會乖乖待在一個人身上——它會穿過人跟人之間的空氣，落到下一個人身上，然後在那裡繼續。重點不在「這東…更多收起
比較像：某個東西不會乖乖待在一個人身上——它會穿過人跟人之間的空氣，落到下一個人身上，然後在那裡繼續。重點不在「這東西壞不壞」，而在「它會自己往外跑、會在別人身上接續下去」。From the word’s history
From Latin inficere 'to dye, stain, taint' (in- 'into' + facere 'to do, put'). The old image is of something being put into a substance and colouring it through — which is what a spreading illness, or a spreading mood, does to the next person.
字根來自拉丁文 inficere「染上、沾染」(in- 進去 + facere 做、放)。原本的畫面是把某種東西放進去，讓整塊材料都染了色——傳染病和會擴散的情緒對下一個人做的，正是這件事：不是碰一下，是整個染上。
Wiktionary: infectious < New Latin īnfectiōsus, from Latin inficere (in- + facere)
Two branches
情緒與笑會傳開
把「自己會往外跑、在下一個人身上接續」這個動作從病借給情緒——形式一樣，只是傳過去的東西變成了心情。
quickly spreading (feeling) · adjective · C2
Infectious feelings, laughter, or a smile spread quickly from one person to another.
有感染力的
原始詞典資料4 筆記錄
以下是外部詞典記錄的用法，原文照列，我們還沒有寫成教學內容。上面的說明才是我們自己寫的；有些用法可能上面已經講過了。
infectiousadj/ɪnˈfɛk.ʃəs/
- 1
medicinepathologysciencesCaused by an agent that enters the host's body (such as a bacterium, virus, parasite, or prion); often, also, transmitted among hosts via any of various routes (for example, contact, droplet-borne, airborne, waterborne, foodborne, fomite-borne, or bloodborne).
- Cancer is usually not infectious.
- More infectious diseases like the flu are usually less potent.
- 2
medicinepathologysciencesAble to infect others; capable of transmitting pathogens.
- Despite feeling better, the patient is still infectious.
- I doubt that [saliva] is very infectious ... I don't think this is a normal route of transmission.
- 3
Spreading quickly from one person to another.
- infectious smile
- Her enthusiasm for work can be really infectious.
- 4
informalMemorable and invoking excitement or interest.
- Pop music is more infectious than elevator music.
資料來源：英文維基詞典 English Wiktionary（CC BY-SA 4.0）。 原文照列，未經改寫。