בא אל פרעה (בא י: א) – “Bring to Pharaoh”

By all other מכות (plagues), the pasuk says that when Hashem commanded Moshe to bring on a מכה, it says which מכה would come.  This pasuk doesn’t clearly say what מכה will come now.

However, we do see it hinted in the word בא.  The letters א and ע are interchangeable since both letters’ pronunciations are from the throat.  And the letters פ and ב are interchangeable, too, as they’re both pronounced through the lips. 

If so, we can take the word פרעה and interchange the פ and the ע for the ב and א, it spells out ארבה. The pasuk comes to imply בא אל פרעה – bring to פרעה the letters ב and א which spells the plague ארבה.