If the Ba'al Koreh missed even one word or even one letter, regardless if omitting that word or letter changes the meaning of the Posuk, he must go back to the place where the mistake was made and re-read from there again. (In certain instances, such as if the missed word changes the meaning of the Posuk, and he was Masiach Da'as from the Megilah, a new Bracha may be necessary too)
Similarly, one who is listening to the Megilah must be very careful not to miss hearing even one letter of the Megilah.
2) If one did miss hearing a word or letter of the Megilah (as is common when someone coughs, or is a child makes noise etc.) the listener must read the missed words by him/herself until he/she catches up to the Ba'al Koreh.
L'Chatchila, this should be done from a Kosher Megilah, or at least from a printed Chumash, but definitely not by heart. (See Mishna Berura Siman 689:19 and 690:19)
If a word was mispronounced, in such a way that the meaning of the Posuk was not changed, it need not be repeated L'Chatchila. If the mispronounced word does change the meaning of the Posuk, it is as if that word was skipped, and the Halachos of a skipped word apply.
QUESTION & ANSWER CORNER:
Reader Submitted Questions of interest on topics related to Halachos we covered, as well as other interesting topic and my Answers. Taken from the Q & A page on the Halacha For Todaywebsite. For study purposes only, NOT for Psak Halacha. Questions can be emailed to Halacha For Today)
Reader's Question:
If one is fleishig can he eat parve products made with dairy equipment?
My Answer:
If the parve food cooked in the dairy pot is not a davar Charif (sharp food such as an onion, garlic etc.) it may be eaten even though you are fleishig.
If the food, however, is a davar Charif it becomes milchig according to all opinions if the pot was used within the past 24 hours, and according to some opinions even if the pot was not used in the past 24 hours, therefore it is best not to eat the food while you are fleishig. (Based on Pri Megadim brought in Darchei Teshuva Siman 89:42 and Yad Yehuda 89:5)
Our holy sages, the Chazal tell us
תנא דבי אליהו כל השונה הלכות בכל יום מובטח לו שהוא בן עולם הבא, שנאמר הליכות עולם לו, אל תקרי הליכות אלא הלכות - one who studies [at least two] Halachos daily is assured a portion in Olam Haba - the world to come. (:מגילה כ"ח )