What facts of Dr. robinsons murder do Tom and huck not know about as they flee from the graveyard?

Not knowing that Injun Joe is attempting to frame Muff Potter for the murder, the boys decide to not tell a soul about what they had seen for fear that Injun Joe would seek revenge upon them as well. Their silence shows that they have not yet realized the gravity of their situation. They sign the contract in blood, half mimicking the actions of pirates or robbers. They don't realize the gravity, or reality, of their situation ­ or the situation that Muff Potter will soon be in. Twain uses the howling of the stray dog to foreshadow Muff's misfortune.