Hunden ser sig selv i spejlet.

Because hunden means the dog, while hund means a dog or just dog in a general sense.

Danish usually puts the definite article at the end of the noun:

• en hund = a dog
• hunden = the dog

So in this sentence, Hunden ser sig selv i spejlet, the speaker is talking about a specific dog: the dog sees itself in the mirror.

In Danish, the is often attached to the noun as an ending instead of being a separate word.

Here are the basic patterns:

• en hund = a dog
• hunden = the dog
• et spejl = a mirror
• spejlet = the mirror

So instead of saying something like the dog, Danish says dog-the: hunden.

No, Danish verbs are much simpler than English verbs in this way. The verb usually does not change depending on the subject.

So:

• jeg ser = I see
• du ser = you see
• hunden ser = the dog sees
• vi ser = we see

The form ser is the present tense of at se = to see.

Because sig is the reflexive pronoun used when the object refers back to the subject of the clause.

In this sentence, the subject is hunden, and the dog is seeing itself, not some other animal. Danish uses sig for that kind of meaning:

• Hunden ser sig = The dog sees itself

If you used ham instead, it would normally mean the dog sees him — someone else, not itself.

So:

• sig = reflexive, referring back to the subject
• ham/hende/den/det = ordinary object pronouns, usually referring to someone or something else

Yes, sig alone can often be enough, but selv adds emphasis.

• Hunden ser sig i spejlet = The dog sees itself in the mirror
• Hunden ser sig selv i spejlet = The dog sees itself in the mirror / the dog sees its own self in the mirror

In many contexts, English naturally uses itself, and Danish often uses sig selv to match that strong reflexive idea. Selv makes it clearer and more emphatic that the dog is seeing its own reflection, not just looking in a direction where it happens to be involved somehow.

Yes, in normal Danish grammar, sig refers back to the subject of its own clause.

So in Hunden ser sig selv, sig refers back to hunden.

This is one of the main jobs of sig: it tells you that the subject and the object are the same person, animal, or thing.

A learner should remember:

• sig = reflexive, linked to the subject
• it is usually used in the third person
• it can mean himself, herself, itself, or themselves, depending on context

Because spejl is a neuter noun in Danish, so it takes et in the indefinite form and -et in the definite form.

• et spejl = a mirror
• spejlet = the mirror

Compare that with a common-gender noun like hund:

• en hund = a dog
• hunden = the dog

So the ending depends on the noun’s grammatical gender:

• en-word → definite -en
• et-word → definite -et

Because i is the normal preposition for in in Danish, and with mirrors Danish says i spejlet, literally in the mirror, where English says in the mirror too.

So:

• i spejlet = in the mirror

This is the standard expression for seeing something reflected in a mirror.

This sentence has the basic Danish main-clause word order:

Subject + Verb + Object + Adverbial

So:

• Hunden = subject
• ser = verb
• sig selv = object
• i spejlet = adverbial/prepositional phrase

That gives:

Hunden ser sig selv i spejlet.

This is a very typical and natural Danish sentence structure.

Yes, that is also possible.

• Hunden ser sig i spejlet = The dog sees itself in the mirror
• Hunden ser sig selv i spejlet = a slightly stronger, more explicit version

Using selv makes the reflexive meaning more emphatic. In a sentence about mirror reflection, many speakers naturally like sig selv, because it strongly highlights that the dog is seeing its own image.

A useful way to learn them is:

• hund / en hund = dog
• spejl / et spejl = mirror
• at se = to see
• sig = reflexive pronoun
• selv = self

For Danish nouns, it is especially helpful to learn them together with en or et, because that tells you how they behave later:

• en hund → hunden
• et spejl → spejlet

That makes it much easier to build correct sentences on your own.