The global comparison, taken on its own, seems a rather simplistic and inflexible heuristic: for any pair of phonemes xy, either a word boundary is always hypothesized between x and y, or it never is. Clearly, there are many cases where x and y sometimes straddle a word boundary and sometimes do not. The heuristic also takes no account of lengths of possible words. However, the local comparison may take length into account too much, disallowing words of certain lengths. In order to see that, we must examine<cite> Brent's (1999a)</cite> suggested implementation of Saffran et al. (1996) more closely.