Folge 18.

The Sesame Street character has fun singing some catchy new songs (you and your toddler just might, too), explaining the difference between light and heavy, having a laugh over pictures and numbers, and sharing the screen with a good-natured Whoopi Goldberg and Julia Roberts. Of the various Elmo videos, this one really does have the choicest material and stands up to repeat viewings--a big plus with little ones.