The article explores the problem of an adequate understanding of the Russian speech by foreigners and identifies the difficulties that foreigners have in a situation of cross-cultural communication. As is well known, language skills are not enough for successful communication. Even if a foreigner has very good language skills, it does not always save him from mistakes in speaking and understanding. Why is this happening? It is logical and understandable why a foreigner does not understand texts full of Russian idiomatic expressions, proverbs, sayings, standard expressions from books, films, etc. But why a foreign student who understands a very complex professional texts without any problems can become completely helpless when speaking to a native speaker or reading modern media? In our view, this paradox is explained by the fact that in professional texts there are almost no linguistic elements expressing subjective modality. Any misunderstanding is associated eventually with problems of adequate understanding of the subjective modality. And the greatest difficulties begin when the text contains the so-called "small" (discursive) words. All of this has defines the authors' interest in the problems of the functional-communicative description of such words and in the revealing of the difficulties that may await a foreigner when meeting with such words. In the article, the authors identify the main features of these words, which make them so difficult for foreigners to understand and assimilate, and also classify them in terms of content, form, categorical belonging, positional variability, using as a component of the phrase, as well as verbal and phrasal stress. The study showed that the main difficulties are that these words do not obey the formal criteria by which they can be assigned to one or another part of speech (depending on context, they have a fluctuating categorical identity), all their meanings are context-related, they do not often have a context-neutral meaning in general. The material of the study was taken from colloquial speech, from specific situations that arise when teaching foreigners Russian as a foreign language, as well as data from dictionaries. After processing, a final list of such words was formed. On the basis of this list the authors developed methodological materials, including the semantization of these words in various contexts. Noting that the authors did not intend to teach foreigners to use these lexical units in speech, they only wanted to help foreign students understand these words in different environments. To assess the effectiveness of such approach, an experiment was conducted. The thought experiment was to compare students' understanding of these words before and after passing the special course "Discursive words in the Russian language". The results of the experiment were summarized in the diagram presented in the article, which clearly demonstrates that a special study of "little words" can significantly expand the communicative competence of foreigners and improve their understanding in communication with native speakers.