In this week's Lightning Round, Neil Patrick Harris and Billy Eichner take to the streets to find out how New Yorkers feel about the end of the series How I Met Your Mother.

The great white shark and killer whale are both infamous marine predators. Normally they leave each other alone, but one day, biologists off the cost of California witness something unprecedented.

Over the course of human history, thousands of languages have developed from what was once a much smaller number. How did we end up with so many? And how do we keep track of them all? Alex Gendler explains how linguists group languages into language families, demonstrating how these linguistic trees give us crucial insights into the past.

Jimmy Fallon can't believe he's at the White House on the Fourth of July. Watch part of his stand-up performance from that evening in which he does impressions of ten other comedians!

Learn about the states of matter, solids, liquids and gases, how they're different and where they're found in everyday life.

American singer Christina Perri sings her hit "Jar of Hearts," a song about heartbreak. She is a rising star in the United States and ready to take on the world at large.

Sigrid talks about some of the ways she learned how to speak Italian and French.

We all know that whales are endangered due to hunting and pollution, but do you know how important they are for the ocean and the environment? This video shows how essential a healthy population of whales is to the ocean ecosystem. Creative Commons Attribution license (reuse allowed). Video was not modified. Please visit sustainablehuman.org for credits and more information.

With the Rainforest Alliance certification, everyday purchases can help prevent deforestation and climate change, protect wildlife, alleviate poverty and transform business practices. Choose products with the seal of the green frog when purchasing coffee, cocoa, tea, flowers, fruit, paper, and wood products.

Taylor Swift reflects back on the tour for her album 1989, which was attended by over two million fans. Featuring behind the scenes footage and performances of the song "New Romantics."

Have you ever wondered why English seems to have roots in so many different languages? Here is a look at what words the Anglo-Saxons and Vikings brought to the English language.

The cover letter is an essential document when submitting a job application. Here you can learn about what function a cover letter should serve.

This dazzling short film references the Rosetta mission of the European Space Agency, which intends unlock the mysteries of the comets and, in doing so, the origins of our Solar System.

Katie performs "I Will Be There" - the first single from her new album Ketevan.

Sigrid describes her time in Basel, and how she ended up visiting France and Italy as well.

When we look at insults used in Shakespeare's play "Romeo and Juliet," we get a new insight into dynamics between the characters and how they relate to the development of the story.

When Penny returns from visiting her family in Nebraska, Leonard is happy to see her. Sheldon, however, is much less welcoming when he learns that her family has the flu.

Here is Australian rock band INXS's single "Freedom Deep" from their 1993 album Full Moon, Dirty Hearts. Enjoy!

Sigrid begins her tale of how she ended up in Italy, where she's now living. She was born in Minneapolis and raised in New York. As a young adult, she relocated to Switzerland in order to study early music. In this video, she talks about traveling to Europe for the first time and learning about the different genres of music prior to the classical era.

Leonard finally tells Penny how Sheldon saved his life and broke the elevator at the same time.

The President and First Lady kick off an evening of poetry, music, and the spoken word at the White House.

In this interview from 2004 with Jimmy Carter, budding American film actress Carmen Electra describes her life as being in the middle of a tornado. Enjoy!

Miss World 2013 Megan Young from the Philippines continues her tour of London!

Rozalia Project knows all about marine debris. Do you? Take a look at their wrap-up video from Expedition CLEAN on the Gulf of Maine in August of 2014.