Learn Hardcore German: Pass auf, sonst stolperst du über die Wurzel. - Watch out, otherwise you’ll trip over the root.

Infinitive: aufpassen = to pay attention / to watch out
In a main clause, the prefix auf- separates and goes to the end:
- Ich passe auf.
- Du passt auf.
In the imperative, you also separate it:
- Pass auf!

So Pass auf! is the normal imperative form of aufpassen.

Why is there no du in Pass auf?

German imperative sentences usually leave out the subject pronoun.

So instead of saying:

German normally says:

This is just like English often saying Watch out! instead of You watch out!

If you do include du, it sounds more marked or emphatic:

But in a normal warning, Pass auf! is the standard form.

Why is it Pass and not Passe?

Pass auf, sonst stolperst du über die Wurzel.