Apparently growths like the one Percy developed can be caused by certain flea products,particularly Hartz. I only gave him Hartz once I hope I didn't... Can I get compensation if this turns out to be the case? I've scheduled a vet appointment.
You'll need to the vet to confirm that this is from the product...which most are hesitant to do. They usually will say something like that's a possibility, but rarely can they confirm it was definitively from the Hartz. You should contact the company as well. Every company has a different policy.