Osgood provides a comprehensive examination of every reference to Seaman (long misread as “Scannon” until James Holmberg’s correction), Meriwether Lewis’s Newfoundland dog who traveled the entire length of the expedition. The article traces Seaman’s purchase in Pittsburgh for $20 in 1803 through his documented adventures: catching squirrels, being bitten by a beaver, being coveted and nearly stolen by Native peoples, and suffering from mosquitoes and prickly pears alongside the human members of the party. Osgood analyzes what Seaman’s presence reveals about Lewis’s character and the expedition’s daily life, noting that Lewis’s expressions of affection for the dog are among the most personal passages in his journal. The article also addresses the mystery of Seaman’s ultimate fate, as references to the dog cease in the journals after July 1806, leaving his end unknown.