This film is included in the "Eclipse Series 33: Up All Night with Robert Downey Sr." DVD set.
During President Garfield's "death" scene, shots of actor John Garfield are interspersed throughout. This is a clever visual pun, since John Garfield was famously beloved by women during the Golden Age of Hollywood and died tragically young.
Allen Able, the man man promoting clothing animals, plays himself. Able was a famous practical joker, and his SINA hoax actually fooled enough people to get him a serious interview on The Today Show in 1959. (The original prank was primarily about media censorship, but took on a life of its own as people fell for it.)