Pumpičkou nafouknu duši.

Pumpičkou is the instrumental singular of pumpička.

In this sentence, the instrumental case shows the means or tool used to do something:

• Pumpičkou nafouknu duši. = I’ll inflate the inner tube with a pump.

This is very common in Czech:

• Píšu perem. = I write with a pen.
• Jedu vlakem. = I go by train.

So pumpičkou answers the question with what?

Yes. Pumpička is a diminutive form of pumpa.

• pumpa = pump
• pumpička = little pump / small pump

In real usage, pumpička is very natural for a bicycle pump or a small hand pump. Diminutives in Czech are often not just about size; they can also sound more everyday and natural.

So here pumpičkou most likely means with a small pump / with a bicycle pump.

Because duši is the accusative singular form of duše.

The noun duše is feminine, and in this sentence it is the direct object of the verb nafouknu.

Basic pattern:

• duše = nominative singular
• duši = accusative singular

So:

• Duše je prázdná. = The inner tube / soul is empty.
• Nafouknu duši. = I’ll inflate the inner tube.

Yes, it does. Duše can mean:

• soul
• inner tube (for a tyre)

This is a vocabulary trap for learners, because the same word has two very different meanings.

In this sentence, the meaning is clearly inner tube, because:

• nafouknout means to inflate / blow up
• pumpičkou means with a pump

So the context strongly points to inner tube, not soul.

Nafouknu is the 1st person singular form of the perfective verb nafouknout.

In Czech, perfective verbs do not normally express a present ongoing action. Their present-form endings usually refer to the future.

So:

• nafouknu = I will inflate / I’ll blow up
• not I am inflating

Compare:

• nafukuju / nafukuji duši = I am inflating the inner tube / I inflate it regularly
  (imperfective)
• nafouknu duši = I will inflate the inner tube, one complete action
  (perfective)

So the sentence refers to a completed future action.

The dictionary form is nafouknout.

A rough breakdown is:

• fouknout = to blow
• na- = a prefix that often adds the sense of doing something onto / up / sufficiently / to completion, depending on context
• nafouknout = to inflate, blow up

Then:

• nafouknu = I will inflate

This -nu ending is normal for some Czech verbs of this type in the 1st person singular.

In Czech, the subject pronoun is often omitted because the verb ending already shows who the subject is.

Here:

• nafouknu = I will inflate

So já is not necessary.

You can say:

• Pumpičkou nafouknu duši.
• Já pumpičkou nafouknu duši.

Both are correct, but adding já usually gives extra emphasis, like:

• I’ll inflate the inner tube with a pump.
  (not someone else)

Czech often leaves pronouns out unless they are needed for contrast or emphasis.

Czech word order is much more flexible than English word order. The beginning of the sentence often shows what the speaker wants to emphasize or set up first.

So:

• Pumpičkou nafouknu duši.
  Emphasis on the tool: With a pump, I’ll inflate the inner tube.

Other possible orders:

• Nafouknu duši pumpičkou.
• Duši nafouknu pumpičkou.

These all express basically the same core meaning, but the emphasis shifts slightly.

Putting pumpičkou first can sound like:

• Using a pump, I’ll inflate the inner tube.
• As for the method, with a pump.

Usually, for the instrument used to do something, Czech most naturally uses the bare instrumental without a preposition:

• Pumpičkou nafouknu duši.

Using s is not the normal way to express the tool here. S pumpičkou more naturally means with a pump in the sense of having one with me / together with a pump, not necessarily using it as the instrument.

So for by means of a pump, the best choice is:

• pumpičkou

not usually:

• s pumpičkou

You would normally use an imperfective verb, for example:

• Pumpičkou nafukuju duši.
• Pumpičkou nafukuji duši.

That means:

• I am inflating the inner tube with a pump
• or I inflate the inner tube with a pump (depending on context)

So the contrast is:

• nafouknu = I will inflate it / I’ll get it inflated fully
• nafukuju / nafukuji = I am inflating it / I inflate it

This perfective vs. imperfective distinction is one of the most important parts of Czech verbs.

Yes, it can be tricky at first.

A rough pronunciation guide:

• pumpičkou ≈ POOM-pich-koh
• nafouknu ≈ na-FOH-knoo
• duši ≈ DOO-shee

A few helpful points:

• ou in Czech is like oh-oo blended together
• š sounds like sh
• Czech stress is normally on the first syllable:
  • PUM-pič-kou
  • NA-fouk-nu
  • DU-ši

In natural speech, nafouknu may sound a bit compressed, but the written form is perfectly regular.

Yes, it is natural and grammatical.

It is a short, ordinary sentence, especially in a context like bicycles, tyres, or repairs. A native speaker would understand it easily.

Depending on context, a speaker might also say things like:

• Nafouknu duši pumpičkou.
• Duši nafouknu pumpičkou.
• Nafouknu to pumpičkou.
  if the object is already clear from context

But Pumpičkou nafouknu duši. is absolutely fine.