Gibbs and O'Brien (1990) argue that the high degree of consistency in speakers' mental images for common idioms indicates that conceptual metaphors play a vital role in constraining the meaning of such expressions. The experiment reported here, which monitors speakers' reading of the stimuli used by Gibbs and O'Brien, seeks to uncover a phonological correlate of the same phenomenon. It is argued here that the highly constrained nature of the source domains from which metaphorically motivated idioms draw their meanings (evidenced, in the Gibbs and O'Brien study, by the consistency of speakers' mental images) causes words internal to such idioms to be highly predictable. This predictability is associated with words carrying a low semantic load, licensing their phonological reduction. The hypothesis that words internal to idiomatic expressions are reduced in duration is confirmed, and this is taken as further support for Gibbs and O'Brien 's' findings that metaphors are to at least some extent active in the on-line processing of idioms. (Daniel Sanford)