what incident happened in Skagway that convinced Mercedes, Hal, and Charles that the load must be lightened before leaving for Dawson, and how did Mercedes behave as she lightened the load?

Two other men from a neighboring camp warn them that the sled is too heavy, but they will not listen. When the sled finally moves,it falls on it's side. Raging at the unfair treatment, Buck leads the team in a run, scattering the belongings even further and running the sled over Hal. Finally taking the advice of those around them, they remove many of the superfluous luxuries, though Mercedes cries over them, and more dogs are added to the team. The journey begins. The new dogs are relatively useless -- Buck can teach them "what not to do," but he can't teach them "what to do."