Si and Am

Si and Am are Aunt Sarah's twin Siamese cats and the secondary and major antagonists from Disney's 1955 film Lady and the Tramp. Both were originally voiced by Peggy Lee. They were later voiced by both Mary Kay Bergman and Tress MacNeille in the sequel; MacNeille now voices them both since Bergman's death.

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 in the climatic scene whatsoever.

Personality
Si and Am are sinister pair of cats who use the love they gain from Aunt Sarah 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 take advantage of Aunt Sarah seeing her as a protector and not a beloved owner.

Physical Appearance
Si and Am are identical seal-point Siamese cats. They are sleek and elegant cream-colored felines with angular, wedge-shaped faces and large, blue almond eyes. They have a deep brown facial point with a darker, almost black muzzle, and dark triangular ears. Their noses are black and small, and they both have two middle incisors that hang over their lower lip; these buck teeth are a commonly used Asian stereotype during the late 40s and 50s. Si and Am also have dark brown "stockings" on their front legs and shorter "socks" on their hind legs, and have dark, long, winding tails.

Lady and the Tramp
The two are commonly seen toted in a picnic basket owned by Aunt Sarah, from which they emerge after her brief departure during one scene to perform their trademark musical number, "The Siamese Cat Song" as they wreak havoc throughout the household, damaging property. During the closure of their song, Lady ferociously jumps to chase after them upon hearing of their intentions to sample some of the newborn baby's milk. Collateral damage ensues, and Si and Am feign injury in order to lay all the blame on Lady, who is then muzzled up as a result.

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 Jim Dear and Darling are taking a stroll in town, where they meet up with Aunt Sarah. 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 picnic, 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.

House of Mouse
Si and Am made numerous appearances in the animated series House of Mouse. In "Rent Day" the cats popped out from their picnic basket, cheering for O'Malley and the Alley Cats.

They make a notable appearance in Mickey's House of Villains during the villains' hostile takeover of the club. They are seen singing a part in It's Our House Now!, and later on witnessing Mickey Mouse's climatic battle with Jafar. In the end, the flee with the other villains, after Jafar is sucked into the lamp and defeated.

Disney Parks
Si and Am appear in an extremely large amount of Disney Villains merchandise as well as having a statue of them in the Disney Villains Store in Disney's Hollywood Studios.

Fantasmic!
Si and Am appear in the floating bubble musical sequence. Despite various Disney Villains appearing in the show, they appear without aiding The Queen in her plan to destroy Mickey Mouse. Their roles of not being involved with The Queen are similar to Captain Hook and Governor Ratcliffe.

Trivia

 * While Aunt Sarah was often considered the primary antagonist of Lady and the Tramp, Si and Am went on to become recurring Disney characters, and major members of the Disney Villains franchise.
 * It is indicated that they care for nothing but each other and take advantage of Aunt Sarah, seeing her as a protector, not a beloved owner.
 * These two characters have been cited as Asian stereotypes because of their squinty eyes and bucked teeth (or in their cases, fangs).
 * With their names combined, "Siam" is the former name of the Kingdom of Thailand, referencing the cats' heritage.
 * Si and Am's original names were Nip and Tuck.
 * Si and Am appear in an extremely large amount of Disney Villains merchandise, as well having a statue of them in the Disney Villains Store in Disney's Hollywood Studios.
 * There is some controversy about their gender since it wasn't said during the whole movie, but some fans believe they are female as they're voiced by Peggy Lee, but other fans disagree since Flotsam and Jetsam were voiced by Paddi Edwards and were obviously male