Poll Suggestion: Stories Behind Famous Movie Scenes

Suggestions are welcome, but note that it's not fun facts on scenes in general, but about iconic/well known scenes or sequences. 

In the 1969 movie "Midnight Cowboy,"  a real taxi drove through the blockades and almost hit Dustin Hoffman.  He pounded on the cab and improvised the line "Hey, I'm walkin' here!"  https://www.imdb.com/title/tt0064665/mediaviewer/rm1632274945/

In 1939's "The Wizard of Oz," Buddy Ebsen was originally hired to play the Tin Man.  He had a violent reaction to the silver make-up paint, had to be hospitalized, and almost died.  His role was recast. https://www.imdb.com/title/tt0032138/mediaviewer/rm1845388288/

In "National Lampoon's Animal House," John Belushi's performance in the cafeteria scene was entirely improvised. When he began piling food on his tray, director John Landis urged the camera operator to "stay with him." The infamous "I'm a zit" gag was also improvised, and the reaction from the cast is completely genuine.  https://www.imdb.com/title/tt0077975/mediaviewer/rm1678069248/?ref_=ttmi_mi_128_2