I would say this is a daunting task at the very best, probably not at all suited for perl. Humans can pick up patterns like that with no problem (providing they know the language the patterns are written in), but how does a computer "know" of the word hello? what differentiates "hello" from "hell"? Why is "oh" not part of the pattern??
There needs to be a much stricter rulebase for this to even consider trying it in perl I would imagine, possibly a known dictionary, or small set of specific patterns to look for..
Anyway, my 2 cents..
-Syn0