C. F. Keil and Franz Delitzsch on 1 Samuel 21:12-13

1Sa 21:12-13

But David took these words to heart, and was in great fear of Achish, lest he should treat him as an enemy, and kill him. In order to escape this danger, “he disguised his understanding (i.e., pretended to be out of his mind) in their eyes (i.e., before the courtiers of Achish), behaved insanely under their hands (when they tried to hold him as a madman), scribbled upon the door-wings, and let his spittle run down into his beard.” The suffix to וישׁנּו is apparently superfluous, as the object, את־טעמו, follows immediately afterwards. But it may be accounted for from the circumstantiality of the conversation of every-day life, as in 2Sa 14:6, and (though these cases are not perfectly parallel) Exo 2:6; Pro 5:22; Eze 10:3 (cf. Gesenius' Gramm. §121, 6, Anm. 3). ויתו, from תּוה, to make signs, i.e., to scribble. The lxx and Vulgate render it ἐτυμπανίζειν, impingebat, he drummed, smote with his fists upon the wings of the door, which would make it appear as if they had read ויּתף (from תּפף), which seems more suitable to the condition of a madman whose saliva ran out of his mouth.