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Hello, this is Dr. Jess. I am so sorry to hear about your experiences with your dog!
I have a feeling what is going on with his skin is not related to his ingestion of rat poison. Do you know the name/brand of the rat poison he had? Were there baits missing that he could have ingested prior to when you found him with the block of poison in his mouth?
The reason I ask this is that the kind of poison that causing blood clotting issues does not act immediately, it takes several days for symptoms to appear, so unless your pet had ingested another bait days prior to you finding him with the block of poison in his mouth, then the bleeding of his gums and the petchiae on his belly could be from a different cause. He wouldn't develop symptoms of bleeding within hours of ingesting the bait.
Also, skin lesions and masses are not seen with anticoagulant rodenticides. These are not a normal side effect.
Here is an article on rodent poisons FYI: http://www.veterinarypartner.com/Content.plx?P=A&S=0&C=0&A=1765