Avus pectinem suum nusquam in cubiculo invenit.

Because avus is in the nominative singular, the case normally used for the subject in Latin.

So in this sentence:

• avus = grandfather
• it is the person doing the action of invenit

Latin often shows grammatical roles through endings, not mainly through word order.

Because pectinem is in the accusative singular, which marks it as the direct object of the verb.

Here, the thing being found is the comb, so it must be in the accusative:

• dictionary form: pecten
• in the sentence: pectinem

This is a third-declension noun, and third-declension masculine nouns often have -em in the accusative singular.

Because suum is the reflexive possessive adjective. It refers back to the subject of the sentence.

So pectinem suum means his own comb, where his refers to avus.

Compare:

• suum = his own, her own, their own, referring back to the subject
• eius = his/her, referring to someone else, not the subject

So if the sentence used eius, it would suggest that the grandfather is looking for someone else’s comb.

It refers to avus, but it agrees grammatically with pectinem.

That is a very common point of confusion.

• It refers to the owner: avus
• It agrees in gender, number, and case with the thing possessed: pectinem

Since pectinem is masculine singular accusative, the possessive must also be masculine singular accusative: suum.

Nusquam is an adverb meaning nowhere or not anywhere.

It tells us that the grandfather does not find the comb in any place in the room.

Latin often says something like:

• he finds it nowhere

where English more naturally may say:

• he cannot find it anywhere

So nusquam is doing the job of expressing absence of location.

Because in with the ablative expresses location: in or inside a place.

So:

• in cubiculo = in the room / in the bedroom

Here cubiculo is the ablative singular of cubiculum.

A useful contrast:

• in cubiculo = in the room (location)
• in cubiculum = into the room (motion toward)

So the ablative is used because the sentence is talking about where the comb is not being found, not movement into the room.

Because Latin does not have articles like English the and a/an.

So a noun like avus can mean:

• a grandfather
• the grandfather
• sometimes simply grandfather

The exact sense comes from context.

The same is true for pectinem and cubiculo. Latin leaves that information to the surrounding context instead of using separate article words.

This is a very good question, because in normal Latin spelling invenit can represent two different forms:

• invenit = he finds (present)
• invēnit = he found / has found (perfect)

In modern textbooks, macrons may be added to show vowel length, but many Latin texts do not write them. So without macrons, the form is spelled the same.

That means the tense is often decided by context.

Because Latin word order is much more flexible than English word order.

A very common Latin pattern is:

• subject ... object ... verb

So ending the sentence with invenit is completely normal.

Latin uses endings to show who is doing what, so it does not need a fixed English-style order like subject–verb–object.

This order can also give a natural flow:

• Avus introduces the person
• pectinem suum gives the thing
• nusquam in cubiculo adds the setting
• invenit finishes with the action

Yes. Because Latin depends heavily on case endings, the same basic meaning could be expressed in several word orders, for example:

• Avus pectinem suum nusquam in cubiculo invenit
• Pectinem suum avus in cubiculo nusquam invenit
• Nusquam in cubiculo avus pectinem suum invenit

The core meaning stays the same because:

• avus is still nominative
• pectinem is still accusative
• cubiculo is still ablative after in

What changes is usually emphasis or style, not the basic grammar.