Learn Hardcore French: Le chien pose sa tête dessus, puis il regarde en dessous du lit. - The dog rests its head on it, then it looks under the bed.

Poser means “to set/put down” and often implies a gentle, deliberate placing (e.g., hands, head, an object on a surface).
In this context, poser (la/sa) tête is idiomatic.
Mettre is broader (“to put”), but mettre la tête is not idiomatic; prefer poser la tête or appuyer la tête (“to rest/lean your head”).

Why is it sa tête and not la tête?

Both occur. With body parts, French often uses the definite article after reflexive verbs (e.g., Il se lave les mains).
Here the verb isn’t reflexive, so the possessive is common: Il pose sa tête sur….
You will also see Il pose la tête sur… when the owner is obvious from context; both are natural.

Does sa agree with the dog (le chien) or with tête?

With the noun possessed. Tête is feminine, so it’s sa tête, regardless of the dog’s gender.
Examples: son oreille (ear, feminine but starts with a vowel → son for euphony), ses pattes (plural).

What does dessus refer to? Do I need to name the thing?

Dessus is a pronominal adverb meaning “on it/on top.” It stands for something known from context (e.g., a cushion mentioned earlier).
If the object hasn’t been mentioned, dessus will feel vague. Name it with sur + noun: …pose la tête sur le coussin.

Can I use sur instead of dessus?

Yes, when you name the surface: Le chien pose la tête sur le coussin.
If you want a pronoun instead of repeating the noun, you can use:
- dessus: Le chien pose la tête dessus (“on it”).
- y: Le chien y pose la tête (“there/on it”)—natural if the place/thing is clear.

Is dessus de correct?

Not as a preposition. Say sur + noun: sur la table, not “dessus de la table.”
But as a noun, you can say le dessus de la table (“the top/upper side of the table”).

What’s the difference between sous, en dessous de, au-dessous de, and dessous?

sous + noun: the most direct, everyday “under”: sous le lit.
en dessous de + noun: “underneath/below,” a bit heavier than sous but common: en dessous du lit.
au-dessous de + noun: more formal/spatial (“at a lower level than”), less about contact.
dessous alone is an adverb (“underneath [it]”): Il regarde dessous. With a noun, prefer sous or au-dessous de. As a noun: le dessous du lit (“the underside”).

Is Il regarde en dessous du lit idiomatic, or should it be Il regarde sous le lit?

Both are correct. Regarder sous le lit is the most idiomatic for “look under the bed.”
Regarder en dessous du lit is acceptable but slightly heavier.

Why du lit and not de le lit?

Do I need the second il? Could I write “…, puis regarde en dessous du lit.”?

In standard French, subject pronouns are not dropped. Repeat il: …, puis il regarde…
Omitting it is limited to headlines/notes/instructions, not neutral prose.

What’s the nuance between puis, ensuite, and alors?

puis: “then/next,” slightly literary-neutral; common in writing.
ensuite: “then/afterwards,” very common in speech and writing.
alors: broad uses; as a sequencer it can feel looser (“so/then”), and it also marks conclusions.

How are dessus and dessous pronounced?

Is poser sa tête dessus the most natural phrasing?

It’s fine and heard in informal contexts. Many would prefer naming the surface: poser (la/sa) tête sur le coussin.
To emphasize leaning, use appuyer (la/sa) tête sur… or poser la tête contre….

Can I replace dessus with y?

Yes, if it refers to a place/thing (not a person): Le chien y pose la tête (“The dog puts his head on it/there”).
Remember pronoun order: il y pose (pronoun before the verb).

Why does the sentence switch from Le chien to il?

To avoid repetition. Il refers back to Le chien. French requires a subject in the second clause, hence puis il…

Can I say regarde dessous le lit?

No, not in standard usage. Use sous le lit or en dessous du lit.
If you use dessous without a noun, it’s fine: Il regarde dessous (“He looks underneath [it]”).
As a noun: le dessous du lit = “the underside of the bed.”

Any spelling/hyphen tips for these forms?