One of the textbook examples often given of the smallest mistake which makes a world of difference is וַיִּיקַץ יַעֲקֹב מִשְּׁנָתוֹ, found in the first עליה of this week's פרשה. If the שוא נע is not pronounced under the ש, it changes the meaning of the word from "from his sleep" to "his learning," from the root of the word משנה, suggesting perhaps that יעקב אבינו, instead of awaking from his sleep, ceased to learn!
However, R' Binyamin Marwick points out that this mistake may not be as grave as it seems. First, we must accept that in judging whether a mistake changes the meaning of a word, we may only consider other words from לשון הקדש. We wouldn't worry that someone mispronounced a word and made it sound like a different English or French word. That said, we might also suggest that the realm of different words is limited to the Biblical lexicon. One might even suggest that it may be constrained to include only word forms found in תורה as נביאים and כתובים include a vastly expanded vocabulary. The evolved language, although it may still be considered לשון הקדש, would not figure into the equation. R' Marwick suggest that the word משנה referring to תורה study is of Talmudic origin and not a biblical word and therefore, this mistake need not be corrected.