The study seeks to establish whether pause frequency and pause duration could inform us about the size of linguistic units stored in the mental lexicon. Pauses are seen as a reflection of cognitive effort in lexical retrieval. The basic assumption is that a particular concept starts activating related concepts in a conceptual network via spreading activation. Pausing is assumed to be rare when spreading activation is at work, i.e. in the recall of multiword, or prefabricated, structures. The results show that pausing was significantly more frequent in connection with lexical search in computed as compared to prefabricated structures, thus indicating that prefabricated structures are stored and retrieved as wholes. The most important implication of the study is that the results give further support to John Sinclair’s proposed ‘idiom principle’, according to which strings that would appear to be analyzable into segments nevertheless constitute single choices.