17. The apparatus of claim 13 , wherein the determining the first series of one or more words related to the at least one first clinical fact comprises: removing a removed word from the first expression to form a modified first expression; evaluating the modified first expression using a medical fact extractor to determine whether the modified first expression expresses the at least one first clinical fact; and when the modified first expression does not express the at least one first clinical fact, determining that the first series of one or more words related to the at least one first clinical fact comprises the removed word.
17. The apparatus of claim 13 , wherein the determining the first series of one or more words related to the at least one first clinical fact comprises: removing a removed word from the first expression to form a modified first expression; evaluating the modified first expression using a medical fact extractor to determine whether the modified first expression expresses the at least one first clinical fact; and when the modified first expression does not express the at least one first clinical fact, determining that the first series of one or more words related to the at least one first clinical fact comprises the removed word. 18. The apparatus of claim 17 , wherein: the first expression comprises two or more words; and the determining the first series of one or more words related to the at least one first clinical fact further comprises performing the acts of removing and evaluating for each of a plurality of words of the first expression to determine the first series of one or more words.