Well, ויפתח יהוה את פי האתון ותאמר לבלעם מה עשיתי לך כי הכיתני זה שלש רגלים Num. 22.28 And YHWH opened the mouth of the jenny donkey, and she said to Balaam: What have I done to you that you have given me blows these three times? Indeed the only speaking animal in the Bible besides the נָחָשׁ is this she-ass! אָתוֹן is the very rare case that there is a unique word for the female animal not related to its male counterpart.
There is a case to be made that the serpent in Genesis 3, though he was called a serpent ( נחש nakhash), was not really a serpent. In ancient times, when people heard an animal speaking in a story, that was the signal that a supernatural being was talking, that is a non-human. My basis for saying that the serpent was not a serpent, that is, not a member of the animal kingdom, is Revelation 12:9...the great dragon was thrown down, that ancient serpent, who is called the devil and Satan...By the way, the tidbit about how ancient people thought was from the Hebrew scholar Dr. Michael S Heiser.
Well, as a mundane person I can only speak about the face meaning of the texts. Your point seems to have been already discussed a long time, as Abraham ibn Ezra reported: ויאמר רב סעדיה גאון אחר שהתברר לו שאין דבור ודעת כי אם באדם לבדו נצטרך לומר כי הנחש גם האתון לא דברו. רק מלאך דבר בשבילם And Rabbi Saadia Gaon said differenty that it became clear to him that speech and knowledge is only in man alone. We need to say that both snake and donkey did not speak. Only an angel has spoken for them. But others say it is no more difficult for G-d to give intelligence to a serpent than to human beings. So who knows...