When you are learning another language, you inevitably make mistakes. It's all part of learning, and can even help you remember how to use certain words, phrases, or grammar correctly. Barbara and Sigrid talk about mistakes they remember and never made again!

Barbara talks about language programs called "dual immersion," student take their various classes in two different languages. She also describes her work as a copy editor.

Movie star Harrison Ford is interviewed before the release of “Captain America,” his first film working with the famous Marvel franchise. He talks about his love for playing new and different roles, and reveals why his characters rarely have a beard or mustache.

Both Sigrid and Barbara like grammar and they talk about some of their pet peeves. The also agree that grammar isn't the most important thing. Using the language to communicate is more important.

Barbara talks about a mistake she made as a language supervisor. Sigrid talks about how people in the U.S. speak English even when they have a very strong accent and it's OK. They both agree that learning with a native speaker of the language is the best way to learn.

Barbara talks about the different jobs she had teaching both French and English. Later, she also had a job supervising teachers of foreign languages, though she notes that these are now referred to as "world languages."

Barbara talks about her studies and other experiences that led to her career as a French teacher. Immersion played a crucial role for both sisters in learning new languages.

Barbara is a retired French teacher who happens to be Sigrid's sister. The two have a conversation about language in general and about how Barbara became interested in the career path she followed.

In the waning light, Paul talks about some safety accessories he dreams of putting on the bike, which is still a work in progress. He also talks about the paint job. All in all, he had fun using his knowledge and also learning new things.

Movie star and straight A student Natalie Portman has homework to do just like any other schoolgirl, and reveals that she sometimes finds herself in the same kind of trouble as a normal teenager.

A 14-year-old Natalie Portman talks with David Letterman and Alec Baldwin about starring in R-rated movies and getting straight As in high school.

Paul goes into detail about what materials he used to construct the electric cargo bike. Some features turned out to be essential, such as the kick-stand.

Gwen Stefani talks about her Christmas album, You Make It Feel Like Christmas, and how Blake Shelton's adjusting to life as People's Sexiest Man Alive.

Building something that works can bring a lot of satisfaction. In this case, it's building bikes. Paul likes figuring things out, and seeing what works and what doesn't. Together with a friend, he embarks on a challenging project: building an electric cargo bike!

Aubrey surprises David Letterman when she reveals the story of the film she's in alongside Hollywood superstar Robert De Niro. The conversation then turns to drinking and the host talks candidly about his past.