"Serio" is also an option. I doubt we have any shorter, fixed reaction for that. Apart from some random sounds, obviously ^.^
pies is in the nominative case psem is in the instrumental case
Okay, so I just started thoroughly reading all these comments, and the nominative and instrumental confuses me. I understand how the gender is decided, but that's really it
Since these are two nouns and not pronouns, could it also be correct to say "Lew nie to pies"?