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The Yip Yips (also known as the Martians or aliens) are characters on the popular American children's television show Sesame Street. They are interplanetary visitors, from the planet Mars (in one of the first skits, as soon as they descend, their first words to each other are "...Not Mars." "Nope."). These creatures, with squid-like tentacles, large eyes, and antennae, materialize into a room and say, "Yip-yip-yip-yip... Uh-huh. Uh-huh", in monotone voices. They come across common objects and, curious as to their names and functions, the Yip Yips consult a book they call "Earth book" which presumably contains information about things on Earth. For example, in one skit the Yip Yips try communicating with a telephone by common greetings such as "Hello", "Greetings", and "Hi there!" unsuccessfully. After each failure they say "nope nope nope". Next they address the phone as a cow, a cat, and then a chicken, only finally learning what it really is when it rings. They "ring" back at it with their voices, clearly pleased to have identified and established communication with it.They marvel at devices such as clocks, telephones and computers. When frightened, each covers its face with the lower part of its jaw while making a distinctive "goom" noise.
In one skit, they struggle to decide what to do with a book, possibly not having acquired their "Earth Book" yet. After trying to eat, smell, and hear the book, a wind picks up and opens the pages. After the Martians had recovered from their shock they began to read the words.
They are "Yip Yipped" by multiple muppeteers including Jim Henson, Frank Oz, Jerry Nelson, Martin P. Robinson, and Kevin Clash. The puppets have a very simple design, controlled entirely by two rods (one for the body and eyes, the other for the front of the mouth). This allows their entire bodies to be seen on camera, appearing to float in the air.
The two Yip Yips seen most often are called "Bob" and "Joe". On the Dutch version, Sesamstraat, the Yip Yips are called "Sjoerd and Hendrik Marsman", referring to the early 20th-century poet Hendrik Marsman. Note that in Dutch, Marsman does literally mean "Martian".
- 1971 — Phone discovery by the Yip Yips
- 1972 — Grandfather clock discovery by the Yip Yips
- 1975 — Radio discovery by the Yip Yips
- 1977 — Ernie wakes up and is unable to find Bert. Ernie imagines that the Martians appeared in the middle of the night and asked Bert to join them in outer space. Bert then enters the room and informs Ernie that he was only in the kitchen making oatmeal. Bert leaves the room and the Martians appear in exactly the way that Ernie had imagined. When Ernie yells to Bert asking what they should do about the visitors, Bert does not believe his story and replies, "Ask them if they want any oatmeal."
- 1987 — As contestants of the Guy Smiley Game Show, Bring that Thing. Guy Smiley addresses them as "Stevie and Jonathan Martian". They need to find three things that involve light. The things that they find are a flashlight, a lamp and the moon. They won a jar of fireflies.
- 1988 — with Kermit, Old MacDonald, various farm animals and the Yip Yips, on a "News Flash" from Old MacDonald's Farm. The Yip Yips arrive in a spaceship.
- 1989 — "Get Along", a song with Kermit, a cow, the Yip Yips, Twiddlebugs and Greasers
- 1990 — Faucet discovery by the Yip Yips
- 1990 — Stars, moon, pigs, Earth discovery by the Yip Yips
- 1991 — "Family" song with the Yip Yips
- 1992 — Wind discovery by the Yip Yips, from a fan
- 1994 — On Sesame Street: 25 Wonderful Years, the Yip Yips audition for Big Bird, then go back to "stars".
- 1996 — "Outerspace Friend", a song by Telly with the Yip Yips
- 1998 — People in a limo with the Yip Yips
- Unknown — Book discovery by the Yip Yips
- Unknown — (early 90s?) Visual appearance in "Brush Brush Boogie" sung by three blue monsters with hair over their eyes and yellow horns, had Maria brushing her hair, someone else using a brush, and the Yip Yips brushing their teeth, though they did not speak.
- 2002 — In the recurring skit "Journey to Ernie", Big Bird occasionally found himself in outer space, where he was helped by a Yip Yip in his search for Ernie.
- 1990 — A Yip Yip contributes its voice to the Old MacDonald Cantata along with three Honkers, a Dinger, and Oscar's pet elephant Fluffy.
- 1986 — Luis walks away from his computer briefly, and the Yip Yips visit during that time and experiment with pressing buttons on the computer. Luis comes back to find that his computer has been changed by someone. Later in the show, the Yip Yips come back and leave a flower on the keyboard, which Luis discovers.
- Unknown — Toaster discovery by the Yip Yips
- Unknown — The Yip Yips observe a man and a woman in love (likely early 90's based on clothing and hairstyles).
- 2012 -- Elmo delivers a pizza box to three Yip Yips on Mars.
Around the time of Sesame Street 's 35th anniversary, licensors finally started to notice and recall the characters. In mid-to-late 2003, Hot Topic led the way with the first-known official Yip Yip merchandising, a "vintage"-look T-shirt with two Martians. This was followed in the fall of 2004 with Gund bean-bag toys. Light switch plates, action figures (by Palisades Toys), and stuffed toys followed. The 2006 Sesame Street calendar features the Yip Yips for November, and they make an appearance on the front cover. Costumes of the characters may be purchased, but these may not be authorized by Sesame Street.
The only real acknowledgement of the characters previous to 2003 was their mention in the 30th anniversary book Sesame Street Unpaved.