You did not see them. So you are in no position to doubt.
Of course, there are room for doubts.
The only times I only see serpent or donkey can talk is through tv or film using animations or cartoons. But in reality, they don't talk in human language.
Since ancient people can record in writing, their written religion texts, included myths, fables and fairytales of their gods and people, and included (A) either animals being able to languages of humans, or (B) humans being able to speak or understand the languages of animals.
The bible, like Genesis 3 and Numbers 22, are no different in that respect, with talking animals, hence ancient fables.
One of the stories of talking animals, is the story called today as the Epic of Etana. It is story about a Sumerian king of Kish, Etana, but the story begin with the eagle and snake, who lived in the same tree.
The eagle talked to the snake, and recommended that they become friends and allies, sharing their food they catch. They agreed and hunt and share food, until the eagle betrayed the snake, and ate her youngs. The snake took its revenge by disabling the eagle, cutting the tendons or sinews of the eagle's wings, and left the eagle to die in the pit.
Etana could not produce a son and heir, because his wife and queen was barren. The sun god Shamash, sent the king to find the eagle, because the eagle could help the king to find herb, that could cure his wife's barrenness.
Etana found the eagle, nursed the eagle back to health. The eagle had the strength to carry his new friend, and fly to heaven, where they will meet a goddess who possesses the healing herb.
The story is fascinating, but it is obvious a fable and myth, where the eagle, snake and king can talk in one language. Although the surviving tablets were written in Old Babylonian (20th - 16th centuries BCE), the story is obviously known to 3rd millennium BCE Sumerians, because a figurine of a man (Etana) mounted on eagle have found, dated to the 24th or 23rd century BCE.
You don't even know what "fable" mean, when you associated science. Scientists are not the ones who believe in talking animals, religious and superstitious people are, especially ones who think animals can talk.
If anyone believed in talking animals, it would be you, since it is obvious that you believe in story of Adam and Eve, literally.