Kurosawa's desire for authenticity for this film led to having the hospital set thoroughly stocked with expensive medical supplies of the time period the film's set in. The drawers that were never referred to or opened on camera, were nevertheless filled with pills.
Before filming the flashback scene were Sahachi is dying in Red Beard's clinic, Kurosawa played the last movement of Beethoven's Ninth Symphony, instructing the cast that this was how he wanted to audience to feel when watching this scene. It was the first scene being filmed for the movie, and helped set the tone for the rest of the film.
Toshiro Mifune usually appeared in several films a year for Toho, doing many cameos and guest roles. However, he chose not to do any that year as he filmed Red Beard, allowing himself to be fully immersed in what would be his last film for Kurosawa.
Akira Kurosawa: [weather] The film is well-known for its snowy sequences. Light-hearted scenes are accompanied by snow. Also, like in most Kurosawa films, rainy weather is present in this movie as well, during the somber scene where Yasumoto meets one of the patients, Sahachi.