Na długi spacer zakładam psu szelki, a w autobusie musi mieć także kaganiec.

For a long walk I put a harness on the dog, and on the bus it also has to wear a muzzle.

Breakdown of Na długi spacer zakładam psu szelki, a w autobusie musi mieć także kaganiec.

• ja: I
• mieć: to have
• pies: the dog
• w: on

Questions & Answers about Na długi spacer zakładam psu szelki, a w autobusie musi mieć także kaganiec.

Why is it na długi spacer and not na długim spacerze?

Because na can take different cases depending on the meaning.

• na + accusative often means for, onto, or for the purpose of
• na + locative often means on / at / during a place or event

Here, na długi spacer means for a long walk, so spacer is in the accusative:

• długi spacer → accusative: długi spacer

Compare:

• Idę na długi spacer. = I’m going for a long walk.
• Rozmawiamy na długim spacerze. = We’re talking during/on a long walk.

So in this sentence, it is about the occasion or purpose: for a long walk.

Why is psu used here?

Psu is the dative singular of pies (dog).

It appears because Polish often uses this pattern:

• zakładać komuś coś = to put something on someone

So:

• zakładam psu szelki literally means I put the harness on the dog
• structure: I put [something] on [someone]
• in Polish: [something]
  • on whom? → that person/animal is often in the dative

Forms of pies:

• nominative: pies
• dative: psu

So psu means to the dog / on the dog in this context.