Glattstrikken og rillestrikken sammenlignes.

Because -en is the definite singular ending for many common-gender nouns in Norwegian. Instead of putting a separate word like the in front, Norwegian often attaches the definiteness to the noun itself.

So:

• glattstrikk = stockinette stitch / smooth knitting

• glattstrikken = the stockinette stitch

• rillestrikk = garter stitch / ridge knitting
• rillestrikken = the garter stitch

In compound nouns like these, the definite ending goes on the last part of the word.

No. They are single compound nouns.

A native English speaker might be tempted to split them up as something like smooth + the knitting, but that is not how they work grammatically. Norwegian very often writes this kind of expression as one word.

So:

• glattstrikk is one noun
• rillestrikk is one noun

Then the definite ending is added:

• glattstrikk → glattstrikken
• rillestrikk → rillestrikken

Sammenlignes is the present passive form of å sammenligne, which means to compare.

Base verb:

• å sammenligne = to compare

Active present:

• Man sammenligner glattstrikken og rillestrikken.
• One compares / People compare the stockinette stitch and the garter stitch.

Passive present:

• Glattstrikken og rillestrikken sammenlignes.
• The stockinette stitch and the garter stitch are compared.

So the -s ending here marks the passive.

Because Norwegian can form the passive without using a separate auxiliary like English does.

In English, you usually need:

• are compared

In Norwegian, one common option is:

• sammenlignes

So the idea of are compared is built into that single verb form.

Another possible Norwegian passive is:

• blir sammenlignet

That is closer in shape to English are being compared or are compared, but sammenlignes is perfectly normal.

Because Norwegian verbs do not agree with the subject the way English verbs sometimes do.

In English, you get a difference like:

• is
• are

In Norwegian present tense, the verb form stays the same regardless of whether the subject is singular or plural.

So you can have:

• Glattstrikken sammenlignes.
• Glattstrikken og rillestrikken sammenlignes.

The verb sammenlignes does not change.

The definite forms make the sentence sound like it is talking about those specific stitch types as established topics: the stockinette stitch and the garter stitch.

That is very natural in explanations, textbooks, knitting instructions, or comparison sections.

If you said:

• Glattstrikk og rillestrikk sammenlignes

that could also be possible in some contexts, especially as a heading or a more general label, but the version with -en sounds more like a full sentence referring to the two known techniques.

Yes. That is also correct.

The two main passive options are:

• sammenlignes
• blir sammenlignet

They are often very close in meaning. The -s passive, as in sammenlignes, is often a bit shorter and can sound slightly more formal, neutral, or written. The blir + past participle passive can sound a bit more explicit and is often common in everyday speech too.

So both are good, but sammenlignes fits very well in informative or instructional writing.

Yes. This is standard Norwegian word order:

• subject: Glattstrikken og rillestrikken
• verb: sammenlignes

So it follows the normal main-clause pattern: subject + verb.

If you moved another element to the front, Norwegian would still keep the verb in second position:

• I denne teksten sammenlignes glattstrikken og rillestrikken.
• In this text, the stockinette stitch and the garter stitch are compared.

That verb-second pattern is a very important feature of Norwegian.

It sounds neutral to slightly formal, especially because of the -s passive.

A sentence like this is very natural in:

• textbooks
• instructional material
• articles
• headings
• explanatory writing

In casual speech, people might more often choose something like:

• Vi sammenligner glattstrikken og rillestrikken.
• Glattstrikken og rillestrikken blir sammenlignet.

But the original sentence is completely natural Norwegian.