*********** My least favorite animal is $ leastFavoriteAnimal $.

*********** (set in another template, leastFavoriteAnimal.st)

*********** Notice that this template file uses CamelCase rather than dashes to separate words. Otherwise there's an error with included templates. So, in general: avoid template file names with dashes or underscores, and just use CamelCase for templates. Numbers are also not allowed.
Try uncommenting the next line and see what you get: $!

Include least-favorite-animal.st: $ least-favorite-animal.st $ !$