I had to deal with something similar my last session
Ceratosaur (int2 dino) vs. a silent image of a Bison created right in front of it. The PCs were already engaged with the creature, and the illusion was created as hope for a breather.
Unfortunately for them, the Ceratosaur has scent. I counted this as its interaction with the illusion, it won the will save, and proceeded to brutalize the PCs.
Generally for low int, think of its primal instincts.
Is it noms, does it smell tasty, does it look tasty?
Is it smaller, less scary, prey?
Ow, it's hurting me. Is it going to kill me? Can or should I run to survive?