Peter Lorre did not receive an Oscar nomination for portraying Joel Cairo in The Maltese Falcon.
Lorre is an interesting case here in that he's not exactly menacing, which I doubt was the point since Spade disarms and knocks out Joel Cairo in his very first appearance. What Lorre does so well is personify the lurid world around the search for the Maltese Falcon. Lorre creates such a innately sinister sense in Cairo just as he propositions Spade for a job, before he has even shown any technical evil side on his part. All Cairo is technically saying at first is that he wants Spade to find the object for him, offering him money, not expecting him to break the law, and he even offers Spade some condolences for his dead partner. Of course everything along with that particularly that smile of his that seems to have such pure malevolence within it. There is such a deviousness in every word that he speaks even the condolence seems two sided in some way. Lorre makes it as though everything about Cairo seems as though he's crawled out a particularly dark place just before he came to enter Spade's office. When he suddenly draws his gun on Spade it would have been far more surprising if he left the office without threatening Spade with death.
Lorre is also just very funny in the part although never does he have a set of punchlines to say. I particularly love after Spade has knocked him out and searched him. Lorre is such a great weasel as he acts though he is apologizing for the whole affair in such a sweet fashion as though everything they had was just a misunderstanding. He even asks for the gun back in such a calm unassuming way with those big eyes of his bringing such a surface earnestness to it he makes you believe that Spade would give him a gun back. This make it all the more hilarious when Lorre switches back to wholly sinister presence as he wants again draws the gun on Spade insisting that he look through his office. Lorre really is a villainous delight any time in which he appears and it is wonderful the dynamic Lorre is able to achieve in the part. He makes Cairo an absolute fiend to be sure, but such an enjoyable fiend to watch. There is another splendid moment where he has a discussion with Spade and Brigid O'Shaughnessy (Mary Astor). He begins so professionally as he inquires about Brigid's knowledge then he delightfully falls about apart into a mess as gets into a fight with her when Spade leaves for a few seconds.
Of course just about the best of everything comes in the final sequence of the film as all the players get into a single room to receive the Falcon. This final scene is perhaps the best example of what makes Lorre's performance so good here. Technically speaking Joel does not have too much to say in this last scene as most the dialogue is given between Greenstreet's Gutman and Bogart's Spade. Lorre though would never let himself be forgotten in the midst of all that. Every little gesture of his adds at least a little something to the scene. Lorre frankly is not okay with just standing in the back as he just adds just the right bit of extra color to the scene. Lorre's knows exactly how far to go as he keep Cairo a considerable presence within the scene while not going so far as to be a distraction either. Again he makes Cairo such a terrific weasel within the frame just the way he whispers into ear has something so eloquently devious about it. I especially like though is how he gives the sold out Wilmer such a cold stare, after Wilmer realizes his position, but then proceeds to give him a warm pat on his back like he's saying "ah don't feel too bad". When Lorre does get his little moment though it's all the better. His reaction to finding the real nature of the Falcon is marvelous as breaks down to almost a crying baby over not getting the treasure, while blaming Gutman. I'd say he only tops this with his next reaction of true inspired happiness as Gutman asks him to come along to keep searching for it. This is outstanding work from Lorre as he makes Joel Cairo such memorable part of the story, and shows exactly how to give a flamboyant performance which only adds to the strength of his film.