Hún lagar rifuna fyrst og saumar síðan annan saum yfir hana.

Because rifuna is the definite accusative singular form of rifa (a tear / rip).

• rifa = a tear
• rifan = the tear (nominative)
• rifuna = the tear as a direct object (accusative)

In Hún lagar rifuna, the tear is the thing being repaired, so it is the direct object, and Icelandic marks that with the accusative here.

Because annan has to agree with saum in gender, number, and case.

• saumur = a masculine noun
• Here it is a direct object, so it is in the accusative singular
• The adjective/pronoun annar (another / second) changes form to match it

So:

• nominative: annar saumur
• accusative: annan saum

That is why the sentence has annan saum.

Hana is the accusative singular form of hún when it means her / it, depending on context.

Here it refers back to rifuna. Since rifa is a feminine noun, the pronoun used to refer to it is feminine too.

So:

• rifa is feminine
• therefore hana = it / her referring to rifuna

In English we say over it, but Icelandic uses the same feminine pronoun form that would also mean her.

Because Icelandic often leaves out a repeated subject in the second part of a coordinated sentence when it is clearly the same subject.

So instead of saying:

• Hún lagar rifuna fyrst og hún saumar síðan annan saum yfir hana

it is more natural to say:

• Hún lagar rifuna fyrst og saumar síðan annan saum yfir hana

The subject hún still applies to both verbs:

• lagar
• saumar

This is mainly because of normal Icelandic clause structure.

In the second clause, the subject is omitted because it is understood, so the finite verb comes first:

• og saumar síðan ...

Then síðan (then / afterwards) follows the verb.

A very literal breakdown is:

• og = and
• saumar = sews
• síðan = then
• annan saum yfir hana = another seam over it

This word order is natural in Icelandic, even though English might more often say and then sews.

They mark sequence.

• fyrst = first
• síðan = then / afterwards

So the sentence is organized as a sequence of actions:

1. Hún lagar rifuna fyrst = she repairs the tear first
2. og saumar síðan annan saum yfir hana = and then sews another seam over it

They help show the order of the steps very clearly.

Yfir can take either the accusative or the dative, depending on meaning.

Very broadly:

• accusative often suggests movement, direction, or something being placed across/over something
• dative often suggests position or location

Here, sauma ... yfir hana means sewing something over/across it, so the accusative hana is used.

This is a common pattern with Icelandic prepositions: the case can change depending on the kind of meaning involved.

Here it is a verb: saumar = sews.

That can be confusing because saumar can also be the plural of the noun saumur (seams / stitches). But in this sentence:

• Hún lagar rifuna fyrst og saumar síðan ...

it clearly functions as the verb, because it follows the conjunction and describes the action done by hún.

So here:

• saumar = verb, 3rd person singular present
• from the infinitive sauma = to sew

They are both in the present tense, third person singular.

• laga = to repair/fix
  
  • hún lagar = she repairs / fixes
• sauma = to sew
  
  • hún saumar = she sews

Icelandic often uses the present tense in contexts where English also uses the present, especially for describing a process, a general action, or steps in a procedure.

Yes. Annar can mean both another and second, depending on context.

In this sentence, annan saum most naturally means another seam / an additional seam. But the idea of a second seam is closely related, and in some contexts that may also be how it is understood.

This is very common in Icelandic:

• annar can express something like one more
• or the second one

The exact nuance depends on the situation.

Yes, possibly. The noun saumur can refer to a seam, and in some contexts something closer to a stitch.

Which English word fits best depends on the real-world situation:

• if someone is repairing a tear in fabric, seam may be a natural translation
• if the focus is on the act of sewing across the tear, stitch or line of stitching may also fit

So a learner should know that the Icelandic word may cover a range that does not match English perfectly one-to-one.

Yes:

• Hún = she
• lagar = repairs / fixes
• rifuna = the tear / the rip
• fyrst = first
• og = and
• saumar = sews
• síðan = then / afterwards
• annan = another / second
• saum = seam / stitch
• yfir = over / across
• hana = it (referring to the feminine noun rifa)

So the structure is very close to:

• She repairs the tear first and then sews another seam/stitch over it.