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 the first skit, as soon as they descend, their first words to each other are "...Not Mars." "Nope."). 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 their skits, 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 their first 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 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".
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 — by the Yip Yips
1988 — with Kermit, Old MacDonald, various farm animals and the Yip Yips, on a "News Flash" from Old MacDonald's Farm. Yip Yips arrive in a spaceship
1989 — "Get Along", a song with Kermit, a cow, the Yip Yip aliens, Twiddlebugs and Greasers
1990 — Faucet discovery by the Yip Yips
1990 — Stars, moon, pigs, earth discovery by the Yip Yips
1991 — "Family" song with Yip Yip aliens
1992 — Wind discovery by the Yip Yips, from a fan
1994 — On Sesame Street's 25th Birthday: A Musical Celebration, 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 didn't speak
2003 — 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
Unknown (80s?) — 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 (presumably early- to mid-1980s based on technological level of computer and those fuzzbuster outfits)
Unknown — Yip Yips encounter a toaster
Unknown — Yip Yips observe a man and a woman in love. (Likely early 90's based on clothing and hairstyles.)
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.
The only real acknowledgement of the characters previous to 2003 was their mention in the 30th anniversary book Sesame Street Unpaved.