“Lemmings do not engage in suicidal dives off cliffs when migrating. They will, however, occasionally, and unintentionally fall off cliffs when venturing into unknown territory…The misconception is due largely to the Disney film White Wilderness, which shot many of the migration scenes (also staged by using multiple shots of different groups of lemmings) on a large, snow-covered turntable in a studio. Photographers later pushed the lemmings off a cliff.“
LMG points the way to an interesting list of common misconceptions over at Wikipedia. “The Inuit do not have a large number of words for snow. One Eskimo-Aleut language studied had four unrelated root words…By comparison, English has many unrelated root words for snow as well: snow, sleet, powder, flurry, drift, avalanche and blizzard.“