Few dogs truly show “zero warning” in advance of a bite; usually the dog is sending lots of signals that people aren't recognizing. Though you do have the option of returning the dog to the shelter or rescue group, it sounds as if you like the dog and would be willing to give him a chance.

Why would a dog bite without warning?

Since dogs are sentient beings like humans, they learn to stop growling in order to avoid physical punishment. ... As a result, when dogs who are trained to hide their growling are pushed too far, they eventually bite without warning. They've unintentionally been trained by owners and/or dog trainers to do this.

Do dogs automatically get put down for biting?

In order to be euthanized, the dog must have bitten people on two separate occasions or caused substantial physical injury after being trained to fight, attack or kill. Still, someone's dog will never be euthanized automatically.