aufschneiden
to cut open
To open something with a knife or scissors, or to cut it into slices.
Könntest du bitte den Kuchen aufschneiden?
Could you please cut the cake?

to cut open / to brag
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to cut open
To open something with a knife or scissors, or to cut it into slices.
Könntest du bitte den Kuchen aufschneiden?
Could you please cut the cake?

'Aufschneiden' (to cut open / to brag) is a separable verb. The prefix 'auf-' comes at the end in a main clause. In subordinate clauses or in the infinitive with 'zu', the verb stays together.
Ich schneide schnell den Apfel auf.
I'll quickly cut open the apple.
In the literal meaning, 'aufschneiden' (to cut open/cut) is often used for food. Typical objects are 'Brot' (bread), 'einen Kuchen' (a cake), 'eine Melone' (a melon), or 'einen Braten' (a roast).
Wer möchte das erste Stück vom Geburtstagskuchen aufschneiden?
Who would like to cut the first piece of the birthday cake?
In the meaning 'prahlen' (to brag), 'aufschneiden' (to brag) is colloquial. In this case, it can also be used without an object.
Er schneidet gerne mit seinem neuen Auto auf.
He likes to show off with his new car.
to open
'öffnen' and 'aufschneiden' can both mean that something is opened. 'öffnen' is neutral and general. You can open a door, a bottle, a bag, or a book. 'aufschneiden' is used when you use a knife, scissors, or another sharp tool. It fits, for example, with a package, a bread roll, or in medicine. Learners may confuse the words because the result is similar: afterward, something is open. The important difference is the method. If you cut, 'aufschneiden' is more precise; without cutting, you usually use 'öffnen'.

Frau Lange schneidet das Paket mit einer Schere auf.
Ms. Lange cuts the package open with scissors.
Er öffnet den Rucksack, aber findet sein Handy nicht.
He opens the backpack but can't find his phone.