Continuity mistake: The plate Buck and Mano wash is a 20th Century pie tin made of non-reflective aluminum, something unlikely to be found in 1870s Arizona. After they dry it off, it changes into polished steel that's shiny enough to reflect their faces. It also changes shape.
Continuity mistake: Victoria is cleaning a lamp and has removed the globe and placed it on the table. After Buck and Mano enter, her blue cleaning rag jumps from hanging on the lamp to being in her hands and back several times between takes. And the lamp globe mysteriously replaces itself by the end of the scene, even though she hasn't touched it again. (00:44:00 - 00:46:30)
Continuity mistake: When Mano wakes Buck up, Buck's hat strings are hanging down over his face. When the shot cuts, though, the strings are immediately tucked back over his ears.