Serbian doesn't just stress syllables - it pitches them
The A1 pronunciation lesson mentions, in one sentence, that standard Serbian technically runs on a pitch-accent system before setting it aside as too advanced for beginners. It is one of the more surprising facts a new learner can hear about the language: Serbian marks not just where a word is stressed, but how - rising or falling, long or short - the same four-way system found in Swedish, Japanese and Ancient Greek, and almost nowhere else in Slavic.