Katten har ont i tassen.

Katten is the definite singular form of katt.

• en katt = a cat
• katten = the cat
• katt by itself is usually more like the dictionary form, not what you would normally use here in a full sentence.

So Katten har ont i tassen means The cat has pain in its paw / The cat’s paw hurts.

In Swedish, ha ont is a very common fixed expression meaning to be in pain or to have an ache.

So:

• Jag har ont i huvudet = I have a headache / My head hurts
• Hon har ont i ryggen = Her back hurts
• Katten har ont i tassen = The cat has pain in its paw / The cat’s paw hurts

A native English speaker may expect a structure built around hurt, but Swedish often uses ha ont instead.

In this expression, ont is part of the fixed phrase ha ont.

Historically, ont is related to ond, but in modern Swedish, learners should usually just treat ha ont as a set expression meaning to hurt / to be in pain.

Important point: in this phrase, you use ont, not a form that agrees with the subject.

So you say:

• Jag har ont
• Du har ont
• Katten har ont

Not ond or ont changing to match katten.

Swedish commonly uses ha ont i + body part.

So the pattern is:

• ha ont i huvudet = have pain in the head
• ha ont i magen = have pain in the stomach
• ha ont i benet = have pain in the leg
• ha ont i tassen = have pain in the paw

The preposition i is the normal one in this construction. English often uses in too in phrases like pain in the leg, so this part is not too strange once you learn the pattern.

This is a very common Swedish pattern with body parts: Swedish often uses the definite form of the body part instead of a possessive like my, your, his, her, or its.

So Swedish prefers:

• Jag har ont i huvudet
  literally: I have pain in the head
  natural English: My head hurts

• Hon har ont i handen
  literally: She has pain in the hand
  natural English: Her hand hurts

• Katten har ont i tassen
  literally: The cat has pain in the paw
  natural English: The cat’s paw hurts

Using sin tass here would sound less natural in ordinary Swedish.

Because Swedish normally uses the definite form for body parts in this kind of sentence.

The idea is that the body part is understood as the one belonging to the subject. So tassen means the paw, but in context it is naturally understood as the cat’s paw.

This is one of those places where Swedish and English organize the sentence differently:

• Swedish: har ont i tassen
• English: has pain in its paw or its paw hurts

Yes, you can. Kattens tass gör ont is also possible and means something like The cat’s paw hurts.

But there is a difference in style:

• Katten har ont i tassen is very common and idiomatic.
• Kattens tass gör ont is more focused directly on the paw as the thing that hurts.

In everyday Swedish, ha ont i + body part is often the most natural way to say this.

It usually means one paw, but not necessarily that the speaker has identified exactly which paw in advance. It just means the cat has pain in a paw.

If you wanted to talk about more than one paw, you would change the form:

• Katten har ont i tassarna = The cat has pain in its paws

So singular tassen suggests one paw, while plural tassarna suggests more than one.

Yes, absolutely. This is a general Swedish pattern used with both people and animals.

Examples:

• Jag har ont i foten = My foot hurts
• Barnet har ont i magen = The child has a stomach ache
• Hunden har ont i örat = The dog has pain in its ear
• Katten har ont i tassen = The cat’s paw hurts

So once you learn ha ont i + definite body part, you can use it in many situations.