What clues does the author of “An Occurrence at Owl Creek Bridge” provide to show that Peyton Farquhar’s escape is only an illusion?

Although most readers fall for Ambrose Bierce's trick and are surprised when Farquhar swings from the bridge after all, Bierce leaves plenty of clues that the escape is imaginary. For example, although senses may be heightened under stress, the exaggerated abilities Farquhar possesses strain credulity. While swimming away in the river, he can see the veins in the leaves of the trees on the shore and the insects upon them. He can see the eye of the sharpshooter looking at him through the sights of the rifle. Though frantically swimming away from the bridge, he can observe the actions of the sentinels on the bridge. A bullet fired at him lodges between his collar and neck, and he snatches it out.
His walk toward home is similarly impossible and contains other hints. He sees a "roseate light" and hears "aeolian harps," both representative of the afterlife. He hears "whispers in an unknown tongue," an allusion to the Bible passage that begins, "If I speak with the tongues of men or of angels." He falls asleep while walking and walks a considerable distance, all night long. By now, readers should be questioning how all this can happen. Unfortunately for Peyton Farquhar, it did not.

In part I of the short story, Peyton Farquhar stands on an unstable wooden board on the Owl Creek Bridge, twenty feet above the rushing water with a noose around his neck. As Peyton is awaiting his death, he attempts to think about his wife and children. However, Peyton is distracted by a loud, obnoxious sound like the "stroke of a blacksmith's hammer upon the anvil." Peyton's ears begin to hurt as a result of the loud, repetitive sound, which turns out to be the ticking of his watch. The reader immediately recognizes that Peyton's senses are heightened and his perception of reality is distorted. Through Peyton's active imagination and heightened senses, Bierce cleverly reveals that Peyton's perspective is illusory. Bierce also comments on Peyton's hopeful thoughts of escaping and returning back to his family at the end of part I.
Part 3 begins as Peyton is struggling to survive in the water and untie his hands in order to swim away. When Peyton finally frees himself, he is able to avoid an onslaught of artillery fire before swimming to shore. On the shore, Peyton describes the sand as diamonds, rubies, and emeralds. He also notices drops of dew on each leaf and notices imperceptible aspects of nature, which corresponds to the heightened senses that he initially experienced while standing on the bridge. On Peyton's journey home, he takes a strange, long, barren road and notices unfamiliar constellations in the sky before he approaches his estate to see his wife, which is the moment when the soldiers execute him. Overall, Bierce's description of Peyton's heightened senses, illusory perception, and strange journey home are clues that Peyton is imagining his escape.