One thread that connects all the Lassie projects is Lassie herself. Every one of the long string of Lassie productions has featured a collie directly descended from the original canine star, a dog named Pal. The new film was made with 8-year-old Lassie the ninth, and three other non-related collies, whose biggest challenge were in scenes swimming across Loch Ness on her way home. "They weren't bred to be water dogs, who have more webbing between their feet and more fat on their body to insulate them for the water," said trainer Carol Riggins, who has steered the Lassie stable through Lassies seven, eight and nine. "Collies don't have that. When you put them in the water, as soon as they get wet to the skin you have to take them out and you have to blow dry them before you can do the rest of the scene. When they get in the water they get cold and their muscles don't work as well."
There were some earlier "Lassies," in literature of the 1800's, as well as in silent films. Eric Knight, a British-born author, wrote a Lassie character in a short story in 1940, then expanded it to a novel called "Lassie Come Home," which became the first Lassie sound film. The original "modern" Lassie was first played by a male collie named Pal in Lassie Come Home (1943). Pal is listed on the IMDb as Pal, and played Lassie in all of the early sound films. His descendants played in the TV series and in most Lassie films and TV appearances since.