That’s all true. Antivenin not antivenom is very expensive and requires large quantities to be effective. More importantly, the antivenin is generally species specific,so what works for one may not be effective for another. Some products, like the fort dodge crotalid polyvalent antivenin can be effective for many species, in this case, most rattlesnakes. That said, most rattlesnake bites are not fatal, not even in dogs. Most of the action from the venom occurs within 2 hours. Administration of antivenin after that window significantly reduces the efficacy. There is the chance of anaphylaxis from the antivenin itself which would normally require that you test a skin pop to see if there is reaction. Rattlesnake bites can cause serious tissue damage and even compartment syndrome in extremity bites. Secondary infections are the real danger 2-3 weeks out. I have administered 12 vials to a large breed dog 3 hours ant the insistence of the owner after he was bitten on the face and front leg. The thing is you never can tell how much, if any, venom was injected. The dog recovered forthwith after the magical $10,000 in treatment. This is purely anecdotal, as i did also witness a jack russel terrier die in 20 minutes from a rattlesnake bite. I know 2 people that have lost fingers to snakebites and one who had major fasciotomy on his forearm to relieve the swelling and compartment syndrome from rattlesnake bite to base of thumb. His arm looked like a black football. So, for Cobra and the like, you maybe don’t need the antivenin so much as a ventilator like pronto! Cobra venom doesn’t cause local damage as much as paralyze your respiration. If someone can breathe for you, you might survive. Better to hack off the finger that was bitten.