I - Chaya I - Chaya was a beloved pet " sehlat " that Spock had in his boyhood . I - Chaya was quite old and had belonged to Sarek during his own youth . ( ) When Spock undertook his " kahs - wan " ordeal prematurely , I - Chaya insisted on following him despite Spock ' s orders against it . It turned out to be a good thing , considering that a " le - matya " – a dangerous animal native to – attacked Spock and I - Chaya . I - Chaya fought the creature as best he could , but the old " sehlat " fell in battle and both he and young Spock had to be saved by the adult Spock , posing as young Spock ' s cousin Selek , who had traveled into the past to prevent his own death at this moment . Although young Spock managed to find a Vulcan healer to help I - Chaya , the " sehlat " was beyond meaningful aid when he arrived . Faced with the choice of a painful extended existence or a peaceful release from his suffering , Spock logically chose to have I - Chaya euthanized . It was an act that marked Spock ' s decision to follow the philosophies of Surak . Spock ' s parents had I - Chaya ' s body brought back from Vulcan ' s Forge , to be buried in a place of honor on the family grounds . ( ) Background information . I - Chaya was partly based on a cat that D . C . Fontana owned , a feline named Bobby McGee as a reference to the song " " . ( " Yesteryear " text commentary ) In , Fontana explained , " " As to who and what I - Chaya would be as a character , I decided he would be closely patterned on my large cat , Bobby McGee . While Bobby is not old and fat , he has the same affection , snuggle - ability , the fastest claws in the West , and complete disregard for orders . ' One word from me , and he does exactly as he pleases . ' The statement fits both Bobby and I - Chaya . " " ( " Babel " # 5 ; " Enterprise Incidents " , number 11 , p . 27 ) The animal is commonly referred to as " Eye - chi - ah " in the final version of " Yesteryear " , although the pronunciation that was originally intended is " EE - chi - ah " and " Yesteryear " ' s script phonetically spelled the name in that way . The name ' s pronunciation was changed during recording of the episode ' s vocals , initiated with an error that the production staff then tried to cover up by changing all readings of the name to " Eye - chi - ah . " D . C . Fontana much preferred the original pronunciation , referring to it as the " proper pronunciation " and remarking , " " The name – always , forever , and correctly – is ' EE - chi - ah . ' The other pronunciation is awkward , ' Lumpy , ' lacking smoothness , and unpleasant to the ear . In short , it is not Vulcan . " " ( " Babel " # 5 ; " Enterprise Incidents " , number 11 , p . 27 ) By way of clarifying how the " sehlat " s name was to be pronounced , the novelization of " Yesteryear " ( in " Star Trek Log 1 " ) commonly spells the name as " Ee - chiya " . In the script of " Yesteryear " , I - Chaya was described thus ; " " This particular " sehlat " has a brown coat frosted with patches of grizzled beige , and one of his worn , yellow fangs is broken off at the tip , indicating he is aging . " " The teleplay additionally specified that I - Chaya had been owned by Spock throughout his ( Spock ' s ) life .