Ibn Ezra on Numbers 5:22

ולנפיל. נפתח הלמ"ד להורות על חסרון ה"א הבנין וכן לשמיד: TO FALL AWAY. The lamed of lanpil (to fall away) is vocalized with a pattach because the heh of the form⁶³The hifil. is missing.⁶⁴Lanpil is short for le-hanpil. The same is true of the word lashmid (to destroy) (Is. 23:11).⁶⁵Lashmid is short for le-hashmid.

אמן. פעמים חזוק: AMEN, AMEN. The word amen is repeated for emphasis.⁶⁶To indicate that the woman fully agrees with what the kohen says.