((Alright, I forgot about this last time, but if I'm reading this correctly, unless your dice roll already accounts for it, you take a -4 penalty to your feint due to acid beasts being non-humanoid. Then you take an additional -8 penalty for them being of animal intelligence (Int of 1 or 2). This would put your end result at 9. (If your roll already accounted for this, then feel free to ignore my ramblings.)))
Sense Motive vs 9 Bluff to Feint
((ETA: Well, what do you know? They rolled poorly enough they still failed.)))
Ryzia fakes out one of the Acid Beasts, but it overreacts to her feint, causing her next thrust to miss.