how does huck know his plan to make people believe he has been killed is successful? what does he witness?

Huck's first indication that the people on the ferryboat are looking for him is when he sees the smoke from the cannon they are firing over the water "trying to make my carcass come to the top". Then he sees a loaf of bread that the people had put into the water believing that the quicksilver they had placed in the bread would find his body. Because Huck is knowledgeable about the superstition, he knows they are looking for a dead body. Then he watches as the boat comes close to shore. He sees all the people on board including Pap and hears them talking about the murder.