Adam Clarke on Numbers 22:28

The Lord opened the mouth of the ass - And where is the wonder of all this? If the ass had opened her own mouth, and reproved the rash prophet, we might well be astonished; but when God opens the mouth, an ass can speak as well as a man. It is worthy of remark here, that Balaam testifies no surprise at this miracle, because he saw it was the Lord's doing. Of animate and inanimate things receiving for a short time the gift of speech, the heathen mythology furnishes many fictitious examples, with which I do not deem it proper to occupy the reader's time.