Learn Hardcore French: Marie met un petit pansement sur mon doigt pour arrêter le sang. - Marie puts a small bandage on my finger to stop the blood.

Marie met un petit pansement... = present tense
→ She is doing it now / this is what she does.
Marie a mis un petit pansement... = passé composé
→ She put a small bandage on (she already did it in the past).

So choose met if you’re describing what is happening at this moment, and a mis if you’re talking about a completed past action.

Why do we use mettre here? Could we use another verb like poser or coller?

Mettre is the most common everyday verb to talk about putting or applying something, so:

mettre un pansement = to put a bandage on (someone)

You could use other verbs, but they sound different:

poser un pansement – more formal/medical, often used by nurses/doctors.
coller un pansement – literally “to stick a bandage (on)”, emphasizing that it’s adhesive.
appliquer un pansement – more formal, often in written instructions or medical contexts.

For normal spoken French, mettre un pansement is the natural, neutral choice.

Why is it un petit pansement and not un pansement petit?

In French, many common adjectives go before the noun, especially those about:

Beauty
Age
Goodness
Size

A common mnemonic is BAGS. Petit (small) is a size adjective, so it usually goes before the noun:

un petit pansement – a small bandage
un grand chien – a big dog
un vieux livre – an old book

Un pansement petit is not wrong grammatically, but it would sound unusual or poetic/marked; in normal speech you say un petit pansement.

Why is it un petit pansement (indefinite article) and not le petit pansement or du pansement?

Each article would change the nuance:

un petit pansement
→ a small bandage (one, not previously identified; just some bandage she picks out)
This is the normal choice in your sentence.
le petit pansement
→ the small bandage (a specific one that both speakers know about: maybe the small bandage we talked about earlier).
du pansement
→ literally “some bandage,” but for bandages (which are countable objects) you almost always use un pansement / des pansements.
Du pansement would be used in a very specific context, e.g. talking about a type of ointment or bandage material in bulk, which is rare.

So un is used because we’re introducing a (any) small bandage, not referring to a specific one already known in the conversation.

Why is it petit and not petite? Don’t adjectives agree with nouns?

Yes, adjectives in French agree in gender and number with the noun they describe.

Pansement is a masculine singular noun: un pansement.
So the adjective must also be masculine singular: petit.

If the noun were feminine, the adjective would change:

une petite blessure – a small injury
une petite boîte – a small box

Here: un (masc.) petit (masc.) pansement (masc.) all agree.

Why is it sur mon doigt and not à mon doigt or au doigt?

Both sur and à can appear with doigt, but they don’t express exactly the same thing.

sur mon doigt
- Literally “on my finger.”
- Emphasizes contact on the surface of the finger.
- Very clear for something that sits on top of the skin, like a bandage.
à mon doigt / au doigt
- More like “at my finger / on my finger” but less visual; it often behaves like “at” or “to” rather than strongly “on top of.”
- More common with things like rings:
  - une bague au doigt – a ring on (at) the finger.

For a sticking plaster/bandage, sur le doigt/sur mon doigt is very natural because the bandage is directly on the skin.

Why is it mon doigt and not just le doigt, since French often uses the for body parts?

You’ve noticed a real pattern: French often uses the definite article with body parts plus an indirect object pronoun:

Elle me lave les mains. – She washes my hands.
Literally: “She washes the hands for me.”

A more idiomatic version of your sentence using that pattern would be:

Marie me met un petit pansement au doigt.
→ Marie puts a small bandage on my finger (literally: “puts a small bandage at the finger for me”).

In your original sentence, there is no pronoun like me or lui. To make it clear whose finger we are talking about, the speaker uses the possessive:

sur mon doigt – on my finger.

So both are possible, but they use different structures:

With a pronoun → me / te / lui + le/la/les (no possessive adjective)
Without a pronoun → you typically use mon/ton/son, etc., to show ownership.

Is Marie me met un petit pansement au doigt more natural than sur mon doigt?

Both are correct and natural, but they emphasize different things:

Marie met un petit pansement sur mon doigt.
- Clear, simple, slightly more “literal.”
- The focus is the place where the bandage is (on my finger).
Marie me met un petit pansement au doigt.
- Very idiomatic everyday French.
- The focus includes the person (me), using the indirect object me and the definite article au doigt.
- Sounds slightly more “native-like” in many contexts.

If you want very natural-sounding French, Marie me met un petit pansement au doigt is excellent when the speaker is “me.”
If you simply want to describe what is happening without focusing on the grammar pattern, sur mon doigt is perfectly fine.

What does pour arrêter le sang mean grammatically? Why is there an infinitive?

Pour + infinitive is a very common structure in French to express purpose (what something is for / in order to do).

pour arrêter = in order to stop / to stop
pour manger = in order to eat / to eat
pour comprendre = in order to understand / to understand

So:

pour arrêter le sang
→ literally “to stop the blood,”
→ naturally translated as “to stop the bleeding.”

Grammatically it is:

pour (preposition of purpose) + arrêter (infinitive verb) + le sang (direct object).

Why is it le sang and not just sang or du sang?

French uses the definite article le / la / les much more often than English, especially for things like parts of the body and bodily substances:

J’ai mal à la tête. – My head hurts.
Je me suis lavé les mains. – I washed my hands.
Le sang coule. – The blood is flowing / There’s blood.

In arrêter le sang, the idea is “stop the blood (from coming out)”, i.e. stop that blood which is currently flowing. French naturally uses le here.

Other options:

arrêter le saignement – stop the bleeding (more technical/formal)
arrêter le sang de couler – stop the blood from flowing (more explicit)

But arrêter le sang with le is perfectly idiomatic and common.

Can we say pour arrêter le saignement or pour que le sang s’arrête instead of pour arrêter le sang?

Yes, and each option slightly changes the style or emphasis:

pour arrêter le sang
- Very common, neutral, everyday.
- Literally “to stop the blood,” effectively “to stop the bleeding.”
pour arrêter le saignement
- Uses the noun saignement = bleeding.
- Sounds a bit more medical or formal.
pour que le sang s’arrête
- Uses pour que + subjunctive:
  - pour que + le sang + s’arrête
- Literally: “so that the blood stops.”
- More complex grammatically, a little more written or careful style.

In normal spoken French, pour arrêter le sang is very natural and simple.

Could we replace sur mon doigt with a pronoun, like y?

Yes, once the place (sur mon doigt) is clear from context, you can replace it with y:

Marie met un petit pansement sur mon doigt.
→ Marie y met un petit pansement.

Here y stands for sur mon doigt (on my finger).
This works if both speakers already know which place is meant.

Note: if you also have an indirect object pronoun like me, the order is:

Marie m’y met un petit pansement.
(Marie puts a small bandage on my finger.)

This kind of pronoun combination is very common in spoken French, but it’s easier to start with the full forms (sur mon doigt, au doigt) and then learn to replace them with pronouns.