Exodus 7:27

ואם מאן אתה — AND IF THOU BE A REFUSER. מאן — The word has the same meaning as ממאן, refusing, (the Piel participle) only the difference is that it is a description of a person having reference to the action he always does (i. e. it is an adjective and the full phrase would be איש מאן) similar to שָׁלֵו “a man at ease” (Job 16:12); שָׁקֵט “a man at ease” (Jeremiah 48:11); וְזָעֵף [‎סר] “a man displeased” (1 Kings 20:43), whilst מְמאֵן merely describes the person as refusing at some particular moment. נגף את כל גבולך I WILL PLAGUE ALL THY BOUNDARIES — נוגף means smiting. So, too, wherever a form from the root נגף occurs, it does not necessarily denote killing but it may mean merely smiting. Similarly, (Exodus 21:22) “and if they hurt (ונגפו) a woman with child”, does not mean they kill (as the context shows); so, too, (Jeremiah 13:16) “and before your feet stumble (יתנגפו)” (i. e. hit against something); (Psalms 91:12) “lest thou dash (תגף) thy foot against a stone”; (Isaiah 8:14) ”and for a stone of stumbling (נגף)‎”.

וְאִם־מָאֵ֥ן אַתָּ֖ה לְשַׁלֵּ֑חַ הִנֵּ֣ה אָנֹכִ֗י נֹגֵ֛ף אֶת־כׇּל־גְּבוּלְךָ֖ בַּֽצְפַרְדְּעִֽים׃

And if thou refuse to let them go, behold, I will smite all thy borders with frogs: