While primarily known for his directorial prowess, Robert Altman’s brief acting forays offer intriguing footnotes for dedicated collectors. His uncredited yet impactful vocal role as the Mousse in the 1987 animated short *Cat & Mousse* stands out as a unique piece of his filmography. This obscure gem, often found tucked into animation compilations or rare out-of-print VHS tapes, showcases Altman's whimsical side and is highly sought after by completists looking to own every facet of his creative output. Collectors are drawn to these less-explored corners of Altman’s career, valuing the rarity and the historical context they provide within his vast body of work. Unearthing a pristine copy of a film featuring even a minor Altman performance can be a rewarding hunt, offering a deeper understanding of the multi-faceted artist beyond his iconic directorial masterpieces. These ephemeral appearances, like *Cat & Mousse*, represent a unique challenge for physical media enthusiasts, making them prized additions to any comprehensive collection.