how does one discover they're into men or women? i'd say it's the same way for "us".
well, to be honest, it's more or less just my wishful thinking that most ppl "found out" the way i did. just hitting puberty and attraction "already there" just turned sexual too. but it seems that majority of ppl here discovered "it" simply by looking for their next kink... and/or sought it out because they are into "taboo/extreme/degredation/weird" things and not into animals themselves at all.
not to sound like a dick, but you seem to be the latter. your question in itself sounds like you don't believe anyone is into "this" by naturally growing up and is merely one of ppl's kinks hence your "how did you find this?" curiosity.