What if dog eat mouse that ate Tom Cat poision?

You should probably take your dog to the vet. If the dog is large, the toxin in Tom Cat may not be enough to cause problems. Tom Cat uses a neurotoxic chemical and not a blood thinner to kill. If you asked this 3 days ago and you aren't seeing signs of trouble your dog is probably ok. I suggest you at least call a vet and ask them, though.