Dark brown donkey fur is but the beginning of the weird ride coming for Dean and as well soon for Sam.
It is Dean who feels the strange allotment of animalistic sensations that cause his fear to vanish and brings on an arousal he never believe as if it were possible for a man to feel.
Holding himself up off changing arms that soon shall be his forelegs, Dean feels his body swelling, growing, and becoming bestially enhanced. His clothing rips, falling off his changing form. He is hunched over, holding on a railing, his head hands low on by then a much elongated neck.
Turning his misshapenly head, Dean gives a wondering friendly wink to an already changing friend, Sam.
Fear has suddenly stopped and replaced by a building euphoria for the want of being in close proximity to donkey jennets, mares, and any equine female in dire need of a male.
Interestingly to his own strange new sensations, Dean watches with wide eyes and an unabated interest as his donkey shaped maleness unravels, falling downward, it hangs as it swells, becoming a huge heavy hunk of maleness that any male would be proud to own.
A soft braying of Dean to his buddy Sam, and with his donkey erection in full state of arousal, what is then as an animal urges Dean to make his erection sway and swing.