Si and Am

Si and Am are Aunt Sarah's two Siamese cats and antagonists from Lady and the Tramp.

Development
Earlier versions of the storyline, drafted in 1943 during the war, had the two cats appear as a sinister pair, suggesting the yellow peril. They were originally named Nip and Tuck. In Ward Greene's novelization, they tearfully express remorse over causing the Tramp's impending execution by hiding the rat's body as a joke, and then try to make amends, while in the film they do not partake of the climactic scene.

Personality
Si and Am are sinister pair of cats who use the love they gain to get others into a large amount of trouble. The cats are sneaky and love to cause trouble and make messes for their own amusement. It is indicated that they care for nothing but each other and takes advantage of Aunt Sarah seeing her as a protector and not a beloved owner.

Lady and the Tramp
In the film, Si and Am's owner Aunt Sarah is in charge of Lady and the newborn child. While Aunt Sarah is upstairs, the two cats cause trouble downstairs. Si and Am torment Lady and wreck the house claiming it as their own. The cats sing The Siamese Song, and during the song, the cats completely destroy the house and even attempt to eat both the family fish and family bird. They even plan to steal the baby's milk until they are stopped by Lady. Although the cats caused all the trouble, Lady gains all the blame and ends up muzzled by Aunt Sarah, which leads to Lady running away and her adventure begins. Si and Am aren't seen for the rest of the film.

Lady and the Tramp II: Scamp's Adventure
Si and Am reappear in the sequel to the film. They are first seen in the opening of the film while the Browns are taking a stroll in town where they meet up with Aunt Sarah as she claims she will be attending their family picnic as Si and Am love Independence Day. They then appear in Scamp's fantasy as he wishes to be a brave enough dog to take on threats like Si and Am.

In the middle of the film, they are last seen attending a picnic with their owner. During the picin, they are seen attempting to steal the turkey until Scamp arrives and scares them into Aunt Sarah's arms. They are not seen for the remainder of the film.