How does Bill's plea to Sam not to leave him alone with the boy add suspense to "The Ransom of Red Chief"?

In O. Henry's "The Ransom of Red Chief," Bill's plea to his partner Sam not to leave him alone with Ebenezer Dorset's red-haired boy creates suspense because Bill is afraid what might happen to him if he is left alone with the rambunctious boy.
After the two men go into the town of Summit, Alabama, and kidnap the son of the town's wealthy banker Dorset, they eagerly anticipate their gains when they receive the ransom money. However, the young redhead proves to be more trouble than they have expected. The young Dorset "put(s) up a fight like a welter-weight cinnamon bear" as they take him up to the cave. After dark, Bill drives the rented buggy, which they have used for the kidnapping, back to the town of Summit.  He then walks back to the cave. By the time Sam arrives, Bill is pasting "court-plaster" over the scratches and bruises on his face. 
Red Chief has the time of his life at Bill's expense. At daybreak, he plans to scalp Bill, whom he has renamed Old Hank, the Trapper. The boy talks incessantly and excitedly.  Now and then he lets out a war-whoop that causes Old Hank the Trapper, to shiver. "That boy had Bill terrorized from the start." Sam comments. He sleeps fitfully that night and wakes to the sounds of Bill's screaming because Red Chief has a knife and is ready to scalp the terrorized man. After this incident, neither Bill nor Sam sleep for fear of being scalped and burned at the stake.
The next day Bill goes into the town to hear any rumors that are circulating. There is nothing said about the Dorset boy. The kidnappers wonder why the town is so calm. In the meantime, they live in fear. After Bill is ridden like a horse for hours by Red Chief, the man attempts to return the boy to town. But the intimidating boy hikes back to the cave. Desperate to be rid of this maniacal boy who finds his kidnapping an adventure, the men agree to pay the father two hundred and fifty dollars to take back the boy.