Bede

And the woman said to Saul, etc. She calls one seen in the plural, as is very customary in Scripture, where often many are designated by the singular, and singular individuals by the plural number. Finally, when one calf was made, the people said: These are your gods, O Israel (Exodus 32). And not one frog or fly was sent against the wicked, but it is said: He sent among them the dog-fly, and it devoured them; the frog, and it destroyed them (Psalm 77); and countless others of this kind.

Commentary on Samuel ↗