flare is the large mushroom-like shape equine penis makes when the owner ejaculates. it's purpose in horse x horse sex is to drive the ejaculate up the mare's birth canal, because mare's pipework is slopped downwards (or w/e is the correct word for "the canal is higher at her uterus than at her vulva") for self-cleaning purposes.
i'm no expert on the subject, but my guess is that there's no such thing as "unflared horse cock" by virtue of the poor stallion with one being pretty much unable to get a mare pregnant.
lack of the penis flaring is also a good way of spotting crap (commercial) porn, no flare = no orgasm for him. no stallion cums without flaring up.
