John Gill Bible Commentary

Then Sarah denied, saying, I laughed not,.... Some render the words, "Sarah lied" (z); and indeed it was no other than a lie, to say she did not laugh when she did; which she might be tempted to say in her confusion, partly because the back of the speaker was to her, and he could not see her, and partly because it was inward, and very little at least discoverable in her countenance: for she was afraid; of the reproof of her husband; and of the charge of ill manners to a stranger; and especially as she had reason to believe that it was the Lord himself that had spoken these words, and therefore could gladly have excused herself, and wiped off the reproach: and he said, nay, but thou didst laugh; it is not true what thou sayest, for thou didst certainly laugh; this he knew, being the omniscient God, notwithstanding, as he appeared as a man, his back was to her, and though her laughter was more internal than external. (z) "mentita est", Drusius.