In most cases, "mouth" in the Bible represents thought and logic, especially the kind of active, concrete thought that is connected with speech. The reason for this is pretty obvious, but it also holds when people, for instance, remove a stone from the mouth of a well, which represents gaining access to spiritual ideas. The mouth is used for eating as well as speaking, of course. In those circumstances, it represents our first, most external perception of a new spiritual idea or desire. This also makes sense, mirroring the way tasting food in the mouth gives us an instant impression of the quality of the food.

778. Quia nunc ‘aves caelorum’ significant intellectualia vera, ita cogitationes, etiam significant contraria, ut phantasias seu falsa, quae quia sunt cogitationis hominis, quoque aves vocantur, sicut ‘quod impii darentur in cibum avibus caeli, et feris’ pro phantasiis et cupiditatibus, Esai. 18:6; Jer. 7:33; 16:4; 19:7; 34:20; Ezech. 29:5; 39:4. Ipse Dominus quoque phantasias et persuasiones falsi comparat avibus, ubi dicit, Semen quod cecidit super viam duram, conculcatum est, et aves caeli comederunt illud, Matth. 13:4; Luc. 8:5; Marcus 4:4, 15;

ubi ‘aves caeli’ non aliud sunt quam falsa.