Let your Soul not be Desolate

Although mistakes in the הפטרה might not be as serious, they tend to be more prevalent since the reader of the הפטרה tends to be less of a seasoned lainer (depending on the shul.) Unfortunately, there was one year I heard this done completely wrong every time. In the הפטרה of פרשת פרה, towards the end, there are numerous instances of the word נְּשַׁמָּה, meaning desolate. If it is mispronounced נְּשָׁמָה it refers to the soul. Two words, nearly indistinguishably similar whose meanings couldn't be further apart. It would be advisable, if you know who will be laining the הפטרה, to alert them to this in advance. Fortunately, our shul has acquired קלף's for all the הפטרות and now only actual בעלי קריאה lain it.

As MG points out in the comments - for those who are particular about pronouncing a דגש חזק - the דגש in the מ is also an important distinction between the two words.