The alligator on Pearl's farm is named Theda by Pearl, after contemporary star Theda Bara. Bara's stage name has been speculatively noted to be an anagram for "Death Arab" or "Arab Death". Given that Pearl feeds the gator her victims, and that it serves as a direct predator of humans in X, the gator's name being an anagram for "Death" is a perfectly appropriate touch that also makes Theda the reptile into a dual reference to film history—the actress herself, and speculation about her name!
The roasted pig that Ruth leaves outside to rot and become infested with maggots could be a direct reflection of Pearl's own mental state. Pearl's descent into insanity is at least partially blamed on emotional neglect and feelings of rejection, much like how Ruth rejects the pig. Pearl slowly tips more and more into depravity, with her murders being less and less justified, until she's a full blown villain, much like how the pig becomes more and more rotten until its completely inedible.
It's also no wonder that Pearl displays the pig on the dinner table as she welcomes home Howard. It demonstrates the exact type of life Howard will expect; one of dysfunction with a person who has something fundamentally wrong about them that can't be ignored, much like how he can't eat the pig (and probably won't even try).
The The Wizard of Oz allegory doesn't just apply to Pearl, but other characters:
Pearl is a clear stand in for Dorothy, as both are young farm girls with an active imagination. However, she decidedly lacks Dorothy's sweet nature from the start and becomes increasingly comfortable with killing people who inconvenience such plans. The film ends with a twisted take on "There's no place like home," as Pearl's first audition fails and she takes it as the permanent death of her dream, resigned to returning to the farm she didn't then or by the end want to live on.
The scarecrow in the fields, which isn't alive but seems to act as a representation of Pearl's failing commitment to Howard, her sexual desires and ultimately her desire to be loved. In a sense, Howard could be Oz's Scarecrow stand-in; the Scarecrow lacks brains, while Howard openly enables Pearl's horrible acts and doesn't think for himself.
The Projectionist is the Tin Man. While not being made of tin, he metaphorically reflects an industry that can be seen as rigid and mechanical, and his lack of commitment to Pearl and seeing her as just a lay could reflect him lacking a heart in her eyes.
Mitzy is the Lion; blonde, bold and speaks her mind, and ultimately, because of her virtues is killed by Pearl.
Ruth is the Wicked Witch; both are older women who oppose the main character, but while the Witch was evil through and through, Ruth is an Anti-Villain who, while strict and abusive, genuinely seems to want to keep Pearl on the farm to avoid her harming others.
Why does Mitzy not smell the rotting corpses of Ruth or Pearl's father in the house? Well, the place is covered in old food from Pearl and Ruth's fight, and there's a rotten pig outside. Human carcasses are said to smell like rotten pork, and with the pig on the porch, any guests would likely attribute the smell to that.
In a twist of dramatic irony, Ruth inadvertently enabled Pearl to commit an unknown number of murders by insisting she stay on the farm. After all, not only is it isolated from the nearest town with acres of land that make it difficult for victims to escape, but Pearl conveniently has Theda, an alligator who can help her dispose of corpses very easily and make it harder for people to track down victims. X demonstrates that Pearl and Howard have been covering up murders for nearly 61 years. The farm inadvertently became the perfect place for Pearl to cover up all of her crimes.
If Ruth had actually encouraged Pearl to leave, then chances are that, if Pearl ever harmed someone in another place, she'd likely get caught much sooner and face consequences. Part of how Pearl managed to get away with her murders for so long is partially because she has the home-field advantage and knows the terrain more than her victims. Pearl, despite her violence, is deeply emotionally unstable and quite naive, and a common thread between X and Pearl is that her murders are impulsive and passionate, instead relying on the convenience of the farm rather than any calculation or long-term planning. If she had lashed out and killed someone in a highly-populated place like New York City, she'd likely get seen by witnesses and caught rather quickly. By keeping her on the farm, Ruth inadvertently prevented Pearl from ever growing out of her murderous habits.
Considering that Howard as an old man is accepting of Pearl's deranged behavior, it makes one wonder what is exactly wrong with him. Then you remember that he served in two World Wars. He more than likely has some form of PTSD, and it could have desensitized him to his wife's violence.
The nature of Pearl's violence and whether Ruth's behavior/attitude towards Pearl is either the result of trying to curb Pearl's growing violent tendencies or whether Ruth's treatment of Pearl is what encouraged these violent behaviors to begin with leads to two equally horrific possibilities. It leads to a Chicken-and-Egg Paradox of which came first, Ruth's abuse or Pearl's murderous habits, and neither are pleasant to think about as they shift who becomes more sympathetic:
If Pearl was genuinely born a sociopath, then it means that Ruth has spent years handling her husband's failing farm and caring for him while he is incredibly ill and being forced to care for her daughter whose growing more homicidal by the day. In this view, Ruth's bitterness and resentment towards her husband and daughter are much more understandable, and almost makes the blow-up that ends up killing her seem inevitable in the end.
If Pearl was a normal kid at one point, then it's likely that Ruth's behavior is not actually Anger Born of Worry but plain emotional projection based on her own personal failures, and their relationship has likely been this terrible for a while, possibly long before Pearl's father grew sick. In this view, Pearl eventually destroying her family can be seen as a young woman who's grown violent to cope with her dysfunctional and abusive mother, who never responds positively to any of Pearl's good actions anyway.
When Pearl drags her mother to the basement and later invites the Projectionist to the house, he can hear Ruth banging the basement door. Pearl's father is still alive by this point, and probably can hear the banging as well, except, unlike the Projectionist, he knows fully well what's in the basement as he witnessed Pearl and Ruth's fight firsthand. He is basically stuck hearing his dying wife banging for some kind of help and, thanks to his paralysis, is utterly helpless to do anything about it except for listening to her slowly die.
