...כָּל נֵדֶר וְכָל שְׁבֻעַת אִסָּר
First, I am making an assumption which I have been told is not necessarily correct. That is, that the word נֵדֶר as it is pronounced in this פסוק implies סמיכות. If that is the case, the proper pronounciation becomes more crucial than in other instances of סמיכות. Without סמיכות the פסוק would be understood "Every נדר, and every שבועה of אסר..." However, the סמיכות determines that אסר is modifying נדר as well and so it is understood "Every נדר of אסר and every שבועה of אסר..."