Intercomprehension refers to a communication practice in which speakers use closely related languages. We know that the degree of mutual intelligibility differs according to the stimulus modality. This work aims to define the linguistic features which contribute to and impede cross-lingual understanding of speech via production and perception studies involving speakers of four Slavic languages. The current study combines the methodological apparatus from acoustic phonetics and information theory to provide evidence for mutual intelligibility on various levels of language processing. It concludes that the degree of mutual understanding does not always correspond to typological divisions of tested languages. The results presented here suggest that intercomprehension is often driven by unit (un)expectedness rather than the phonetic resemblance of a perceived stimulus and its equivalence in the native lexicon of speakers.