In honor of the 50th anniversary of iconic children's program on Sunday, here is a list of some of the absolute cutest and most heartwarming celebrity guest appearances on "Sesame Street." There are far too many to list them all -- 650 in total -- but here is a smattering of our favorites, from John Krasinski helping Murray define the word "soggy," to Julie Andrews helping Kermit the Frog sing "It Isn't Easy Being Green." Catch a bunch more celebrity guests including Sterling K. Brown and Elvis Costello on Nov. 9 at 7 p.m. during HBO's "Sesame Street 50th Anniversary Celebration," hosted by Joseph Gordon-Levitt.
The "Office" star came on "Sesame Street" in 2011 to help Murray define the word "soggy" -- hint, it means very wet. Little did Krasinski know, he would become the example of what a soggy thing looks like when he gets sprayed with a surprise blast of water from an elephant's trunk. The best part is the into-the-camera look of defeat Krasinski gives at the end, "The Office" style.
Another star of "The Office" came on the show in 2012 to explain what the word "vote" means by asking Abby Cadabby and Elmo to vote for their favorite snack foods. Spoiler: they choose the last-minute third party candidate, pizza.
"12 Years a Slave" star Lupita Nyong'o visited "Sesame Street" in 2014 to help Elmo define the word "skin," which Elmo discovers he has for the first time underneath his red fur. It's a very touching moment.
The "Shape of You" singer visited "Sesame Street" in 2015. He and the Muppets sang a pretty adorable song called "Two Different Worlds" about how to behave at school vs. at home.
Next time you're having a bad day, play this video. Ruffalo, who plays "The Hulk" in "The Avengers" franchise, explains the meaning of the word "empathy" to Murray in a 2011 appearance. But in order to help Murray understand what he's talking about, Ruffalo tells him the story of how he lost his favorite teddy bear, which leads the two collapse into a fuzzy puddle of tears. If that's not the cutest thing you've ever seen, you might need to check your own empathy levels.
The "Happy Gilmore" star visited Sesame Street in 2009, and he brought his guitar with him. As he makes up a song about Elmo, the two brainstorm different words that rhyme with the fuzzy lil' guy's moniker, such as bell-mo, smell-mo, and farewell-mo. This one is also particularly cute because you can tell how much fun Sandler is genuinely having.
The former first lady came on "Sesame Street" in 2014 to convince Grover why he should eat a healthy breakfast every morning... but little did she know that in all his excitement, he would end up eating hers.
The "Trainwreck" star came on the show in 2015 to define the word "grouchy." To get him in the spirit, Elmo and Murray present him with some of his biggest pet peeves: cereal with no milk, when a woodchuck wears his favorite hat, and of course, veggies dancing the polka.
The "Hangover" star came on the show in 2015 to learn what the word "nimble" means. Murray explains it to him by unleashing a piranha muppet so that Zach runs away -- nimbly! -- to avoid being bitten.
The "Master of None" star and Grover wear chicken suits to explain the meaning of the word "ridiculous" in a 2014 appearance. It is exactly that, but in the best possible way.
The "Uptown Funk" singer visited "Sesame Street" way back in 2011 to sing a surprisingly catchy song about the importance of not giving up.
The "Sound of Music" and "Mary Poppins" star visited "Sesame Street" in 1973 for what may just take the cake as the most heartwarming celebrity appearance of them all. She starts by dancing onto the iconic street with a bunch of well-choreographed trash cans, only to be surprised by Oscar the Grouch. Then she makes small talk with Big Bird and helps Kermit sing "It Not Easy Being Green." To thank her, Kermit gives her some roses -- which the Cookie Monster promptly gobbles up.
The supermodel visited in 2014 to sing the ABC song with Abby Cadabby -- until the letter Z comes and interrupts them to complain about how his letter doesn't get enough credit.
The "Seinfeld" star stumbles across Big Bird and a group of kids while waiting for his bus into the city on "Sesame Street" in a 1996 appearance. While teaching them how to play a game that involves jumping up and down, turning around, and then falling down, he gets so distracted that misses his bus. Totally worth it.
In a 2005 appearance, the famous astronaut visited "Sesame Street" to talk about outer space with a little boy named Alex, who declares that one day when he's an astronaut, he'll have a shirt just like Buzz's when he comes to "Sesame Street."
The late poet, singer, and civil rights activist visited "Sesame Street" in 1996 to sing a song with Elmo and two kids named Lexi and Carlo about being proud of their names.
The "Sherlock" actor visited the show in 2014, where Murray decided to rename himself "Murray-arty" and become Cumberbatch's new nemesis. In a truly mind-bending challenge, Cumberbatch enlisted the help of The Count to figure out how many apples and oranges are on the table in front of them.
The "Dirty Computer" singer visited in 2014 to sing a song called "The Power of Yet," all about continuing to try even when things don't work out the first time.
When the "Gravity" singer visited "Sesame Street" in 2009, he declared one thing for certain -- "Nothing cute is about to happen." Elmo agreed. But soon their resolve is broken and cuteness ensues when the pair slowly turn to each other and have a nice hug.