Amid obsessive interest from the media, the producers of "Sesame Street" last week decided not to broadcast a segment featuring a scantily-clad Katy Perry singing a duet with Elmo. (Watch the original clip and Perry's spoof of it on "Saturday Night Live.") Some parents and critics had charged that the combined effect of the pop star's plunging neckline and bouncy antics rendered the performance, previewed on YouTube, unfit for toddlers' eyes. But this dust-up is just the latest episode in a surprising legacy of controversy for the iconic show. Here are ten other cases where Big Bird and company ruffled feathers:

1. The racy years (1969 - 1974)
When it debuts in 1969, the show's rather grown-up content alarms some parents. In a reflection of the era, Cookie Monster puffs on a pipe and Grover takes lessons in civil disobedience from a hippie. The first volume of the show's DVD set now carries an "adults only" warning. (Watch a 1969 clip of Grover and the hippie)

2. Oscar the Grouch's mood swings (1969 - present)
The least cheerful muppet has been regularly called out for being too cantankerous and caustic for preschool-aged viewers. Little known fact: Oscar was originally slated to lead an even more alienated life in a manhole, but "Sesame Street" producers decided to soften him up by switching his home to a trash can. (Watch a youthful Oscar the Grouch sing "I love trash")

3. Elmo's questionable grammar (1979-present)
Elmo's tendency to refer to himself in the third person ("Elmo scared!") raises fears that his small, inchoate fans are learning improper grammar. The show's creators defend the red creature's diction by saying he engages preschoolers who can't yet make sense of pronouns. (Watch "Elmo's song")

4. Bert and Ernie's sexual ambiguity (1980 - present)
Are these two single men who share a bedroom just friends (with color-coordinated orange and yellow skin, respectively) or are they gay lovers? Critics have been registering their disapproval for decades, despite "Sesame Street" producers' assurances that they're not promoting a same-sex agenda. (Watch Bert and Ernie in a cozy, nighttime scene)

5. Mr. Hooper's death (1983)
After actor Will Lee — who played chatty shopkeeper Mr Hooper — dies in 1983, the program pays tribute with an episode that deals directly with death. Wrestling with grief, Big Bird imparts the lesson that life necessarily ends, a theme many parents feel their children are too young to confront. (Watch a clip from "Farewell, Mr. Hooper")

6. A muppet with AIDS (2002)
To fight stereotypes about people with AIDS, "Sesame Street" introduces an HIV-positive muppet named Kami. Some parents protest that their children are too young to face the harsh realities of the virus. (Watch Kami discuss the HIV virus with Bill Clinton)

7. Fears that "Sesame" gives kids ADD (2004)
Some critics say "Sesame Street" is partially to blame for the rise in ADHD diagnoses, noting that the program is broken into 40 short, unrelated segments — the sort of pacing that arguably triggers attention-deficit problems. (Watch a dizzyingly diverting "Sesame Street" clip)

8. Cookie Monster's scandalous diet (2005)

As childhood obesity reaches epidemic levels, "Sesame Street" is skewered for celebrating a blue beast whose defining characteristic is an addiction to baked goods. In 2005, a reformed Cookie Monster begins partaking of healthier choices like fruits and vegetables, prompting rumors that he will be renamed "Veggie Monster." (Watch Cookie Monster gobble down a cookie while singing "C is for Cookie")

9. Mahboub the Muppet (2006)

At the height of the Israeli-Palestinian conflict in December 2006, two versions of "Sesame Street" air in Israel: One for Arab children and one for Israelis. To try to bridge the cultural gap and reinforce the message of tolerance, producers introduce Arab muppet Mahboub into the Jewish version. Though protests ensue, Mahboub soons endears himself to Israelis. (Watch an NBC report about diversity on the streets of "Sesame Street")

10. The program's "liberal bias" (2009)
In a "Sesame Street" segment that appears to mock conservative Fox News, an irate viewer calls the Grouchy News Network (GNN) to complain that the news isn't grouchy enough: "From now on I am watching Pox News. Now there is a trashy news show." After Fox complains, the PBS ombudsman admits that, although the parody was "too good to resist," it "should have been resisted." (Watch Oscar the Grouch trash Fox News)

This article was originally published November 10, 2009 and updated September 27, 2010.