Pass auf, du rutschst auf dem nassen Boden im Flur.

Pass auf means Watch out!, Be careful!, or Pay attention! in this context.

It comes from the verb aufpassen, which often means:

• to pay attention
• to watch out
• to be careful

So in this sentence, Pass auf is a warning.

Because aufpassen is a separable verb.

Its two parts are:

• passen
• auf

In many sentence forms, the prefix auf separates and moves to the end:

• Ich passe auf.
• Du passt auf.

The imperative for du is formed from the verb stem, so:

• aufpassen → Pass auf!

That is why you do not see aufpassen as one word here.

In German, the informal singular imperative usually does not include du.

So:

• Du passt auf. = You are paying attention.
• Pass auf! = Watch out!

Leaving out du is normal and natural in commands.

If you wanted other forms, they would be:

• Pass auf! = to one person, informal
• Passt auf! = to more than one person, informal
• Passen Sie auf! = formal

Because the sentence contains two clauses:

1. Pass auf
2. du rutschst auf dem nassen Boden im Flur

German usually separates main clauses with a comma.

So the structure is basically:

• Watch out, you’re slipping / you might slip on the wet floor in the hallway.

The comma helps show that the warning and the explanation are two separate parts.

German very often uses the present tense to talk about something that is happening now or is about to happen.

So du rutschst can mean:

• you are slipping
• you’re going to slip
• you’ll slip

In warnings, this is very common. German does not need a special future form as often as English does.

So the sentence sounds natural as an immediate warning.

Rutschst is the du form of rutschen.

rutschen means things like:

• to slide
• to slip
• to skid

Here it refers to slipping because the floor is wet.

Form breakdown:

• infinitive: rutschen
• du form: du rutschst

This is a very common learner question.

• rutschen = to slide / slip in a general sense
• ausrutschen = to slip and lose your footing, often on something slippery

In many situations, ausrutschen would also be very natural here:

• Pass auf, du rutschst auf dem nassen Boden aus.

That version stresses the idea of slipping over more strongly.

The given sentence with rutschen is still understandable and natural, especially if the focus is on the dangerous movement on the wet floor.

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

Here the meaning is location:

• on the wet floor

When auf shows a position or location, it takes the dative:

• auf dem Boden = on the floor

If it showed movement onto a surface, it would use the accusative:

• auf den Boden = onto the floor

In this sentence, the person is already on that surface, so German uses dative:

• auf dem nassen Boden

Im is a contraction of:

• in dem

So:

• im Flur = in the hallway

This is very common in German:

• in dem → im
• an dem → am
• zu dem → zum
• zu der → zur

Because Flur is used here as a location, it is in the dative:

• in dem Flur → im Flur

Because the adjective is following a definite article and is in the dative masculine.

Let’s break it down:

• Boden is masculine: der Boden
• after auf with location, we need the dative
• der Boden becomes dem Boden
• with a definite article in this pattern, the adjective takes -en

So:

• nominative: der nasse Boden
• dative: dem nassen Boden

That is why the sentence has:

• auf dem nassen Boden

Because the second part is a normal statement clause, not an imperative.

Compare:

• Pass auf! = command
• du rutschst auf dem nassen Boden im Flur = statement

In a normal German statement, the subject is usually expressed, so du appears there.

It also makes the warning more direct:

• Watch out, you’re slipping...

The basic order is:

• du = subject
• rutschst = verb
• auf dem nassen Boden = location phrase
• im Flur = another location phrase

So it follows normal German main-clause word order, where the finite verb is in second position:

• du rutschst ...

The two place expressions narrow the location down:

• auf dem nassen Boden = on the wet floor
• im Flur = in the hallway

So the full idea is:

• you are slipping on the wet floor
• and that floor is in the hallway

You would change the imperative form of aufpassen:

• to one person, informal: Pass auf, du rutschst auf dem nassen Boden im Flur.
• to several people, informal: Passt auf, ihr rutscht auf dem nassen Boden im Flur.
• formal: Passen Sie auf, Sie rutschen auf dem nassen Boden im Flur.

The rest of the sentence also changes to match the subject:

• du rutschst
• ihr rutscht
• Sie rutschen