Just don't let up. After each feeding of narcotic or biotoxin. You can continue pumping damage into it. If the does the fake raor. Continue to shoot it while it does this. By the end of the fake roar it should do a real one. If you miss a feeding it will go into adrenaline stat. At which point it will NOT go to shield stance and you must wait for it to stop glowing red. I don't usually clear out wildlife as i use them to heal the Acro if I do mess up. Good luck and hope you get the best Acro's!