Context. You could compute the log likelihood ratio of "bye bye" given the previous word versus the log likelihood ratio of "55" given the previous word. If tha

Context. You could compute the log likelihood ratio of "bye bye" given the previous word versus the log likelihood ratio of "55" given the previous word. If that's not good enough you can generalize this to use the previous N words. Google should have a large enough corpus of text at it's disposal to be able to approach the problem this way, and they very well may already be doing so.