Big deal, that. Oh, and, of course, it's a deep-shadowed black-and-white film with deep-focus—a bit standard when dealing with low light levels in black-and-white (especially when the cinematographer is Gregg Toland, who worked on both films). Beyond that, Mad Love is a completely different proposition than Citizen Kane and comparisons between the two are desperate and tortured, (as the writer could be at times).
But, that madness aside, Mad Love is a late version of German Expressionism from the silent era of film, and a direct descendant of:
The Hands of Orlac (Robert Weine, 1928) the silent version, re-teaming the director and star of The Cabinet of Dr. Caligari, Weine and Conrad Veidt. Both stories involve the maiming of a brilliant concert pianist in a train wreck. His fiance, in a desperate attempt to save his career—emplores a surgeon to perform a radical double-hand transplant that has unforseen circumstances. The difference between the two is motivational—in the latter version, the surgeon performs the surgery, not just for the sake of music, but also for his desperate love of the fiancee, an actress in a theater macabre that he devotedly attends every night, going so far as to buy the waxwork figure of her in the lobby as an object of adoration.
The operation is a success, but on the other hand, it isn't. There's just one hitch, the same one that befell Dr. Frankenstein (coincidentally, the pianist in Freund's version is played by Colin Clive, the doctor in James Whale's version)—be careful where you shop for spare parts. In this case, Orlac's hands are replaced by those of a murderer—a strangler in the silent version, a master knife-thrower in Freund's. Before long, the composer is struggling to do his five finger exercises, and working on other handiwork, as well. Before long, he is implicated in a murder, and beset by nightmares that his hands are out of his control (they are, after all, the devil's playground).
The two diverge at this point, with Mad Love concentrating on the insane machinations (literally in one instance) of Lorre's insane Dr. Gogol—in the silent version, the surgeon's role diminishes significantly at this point—and Orlac's new talents become even more literally "handy."
Both versions weigh heavily on the psychological, as Orlac and his new hands lose their grip on reality, but the first one is quite satisfied with takinbg the macabre elements so far. The later version, post-Frankenstein and Dracula relishes the more twisted elements of the subject, going places that the original finds fanciful and, frankly, superstitious. Mad Love embraces the possibility that the murderer's hands will, actually, assert their sense memory allowing Orlac to throw pointy things very, very accurately...and the difference between the two films is only a span of seven years. Interesting how an audience's capacity for the weird and supernatural—and Hollywood's willingness to deliver it—could become so prevalent.
* Freund was the German director/cinematographer whose most enduring influence came in the early days of television production when his 3-camera recording technique revolutionized filmed comedy shows (before a live audience)—a concept that started during his days with "I Love Lucy" but continues to be used today.
** Welles used a super-imposed shot of a cockatiel during what he considered a "rough transition" that didn't have enough dramatic impact, and later joked that he did it "just to wake people up."