You only need 9 fpe to kill a dog size animal . If stealth is a requirement tell your friend to get a .22 cal air gun from Walmart . Most of the newer ones have a built in silencer so they are very quiet to shoot even at night . Hypothetically a person can shoot anytime of the day or night without making a sound . As long as the air gun shoot a 14.3 grain pellet Crosman hollow points and has a MV of around 900 fps and will produce 25 fpe at the barrel and have 9.2 fpe at 114 yards away . So from 0 to 114 yards a 22 cal 14.3 grain pellet will get the job done Hypothetically. With is ruger air rifle https://www.walmart.com/ip/Ruger-Impact-Max-22-Pellet-Air-Rifle/449026134 you get about 733 fps MV what gives you 17 fpe and 9 fpe out to 73 yards . It does have a silencer on it and its pretty quiet . For 140 dollars its a pretty good gun that can be used for squirrel and rabbits once the Hypothetical is taken care of . Watch some youtube video on the gun . A Hypothetical pre dug hole is recommended .