Complex sentence: Possibly his best-remembered film appearance was in Walt Disney's "Mary Poppins" (1964), in which he played an eccentric man floating around just beneath the ceiling in uncontrollable mirth, singing "I Love to Laugh".
Split into simpler sentences: Possibly his best-remembered film appearance was in Walt Disney's "Mary Poppins" (1964). His played an the eccentric man floating around just beneath the ceiling in uncontrollable mirth, singing "I Love to Laugh".