The article attempts to find out what factors could possibly affect the grammatical number of the Estonian words käsi ‘hand’, jalg ‘foot’ and suu ‘mouth’. The material investigated comes from the Electronic Base Dictionary of Estonian Phrases (FES), the Corpus of Modern Estonian Metaphorical Phrases (MetafK) and the Estonian Web Corpus (etTenTen). The article aims to determine (1) the possible differences in the frequency of occurrence of singular and plural forms of the body-part words in idiomatic and non-idiomatic phrases in modern and older language; (2) the possible factors behind the deviations from the normal syntactic and distributional logic of the use of the singular or plural of those words in different sublanguages. In order to find the factors affecting the grammatical number of the body-part terms in question the actual frequencies of the singular and plural forms were counted and, using those results, theoretical frequencies were computed. The statistical significance of the association between word features was tested by chi-square test. It was found that the grammatical number of the body-part words depends on (1) word semantics and (2) specifics of the corpus material. The number preference of the words studied relates to their concrete and abstract meanings, namely, in the investigated corpora käsi (rather) and suu (mostly) occur in the singular, whereas in jalg plural forms predominate. As to corpus influence there seems to be something to do with whether the body-part words are observed in edited idiomatic phrases or sentences or in unedited sentences (no matter if idiomatic or not), although in both cases singular forms are preferred.