The contest here is between Rahel and Ammu's beauty as grown women. A divorced, drifting, and childless Rahel is "longer, harder, flatter, more angular" than her mother had been. Rahel's eyes might be more beautiful, but they are as luminous as her mother's nut-brown skin. This physical luminosity contrasts with their emotional darkness, and makes their lives seem more tragic.
Only her eyes were incontestably more beautiful. Large. Luminous. Drownable in, as Larry McCaslin had said and discovered to his cost.
The example sentences are focused on the physical tightness of Estha's butt. But similar to how Ammu's "watchfulness stretched her, made her taut and tense," Rahel watching her twin brother in this way makes the scene emotionally taut and tense, especially since Estha does not respond.
The sculpted hollows on either side of his taut, beautiful buns. Men’s bums never grow up. Like school satchels, they evoke in an instant memories of childhood.
Seven-year-old Rahel was showing more disrespect ("petulant" also means "contemptuous in speech or behavior") than irritation or annoyance here. In response to this careless petulance on her daughter's part, Ammu deliberately shows her petulance by telling Rahel that she loved her a little less.
“So why don’t you marry him then?” Rahel said petulantly.
"Pugnacious" also means "tough and callous by virtue of experience"--while this can describe a driver whose taxi smells of sleep because it doubles as his home and who jumps lights despite being so small that he looks through the steering wheel, it does not fully describe the nature of a driver who would deliberately try to kill dogs that wander onto the road.
He drove fast, pugnaciously, darting into empty spaces, nudging other cars out of their lanes.
The original plan had been that Estha would sleep with Chacko, and Rahel with Ammu and Baby Kochamma. But now that Estha wasn’t well and Love had been re-apportioned (Ammu loved her a little less), Rahel would have to sleep with Chacko, and Estha with Ammu and Baby Kochamma.
having precise or logical relevance to the matter at hand
"Pertinent" and "local" are used here as antonyms of "grand" and "Maoist"--this gives a negative tone to the adjective "grand" which mocks the "high moral or intellectual value" of the Maoist rhetoric. This is also suggested by the use of the word "rhetoric" ("high-flown style; excessive use of verbal ornamentation" or "loud and confused and empty talk").
In his speeches he managed a clever mix of pertinent local issues and grand Maoist rhetoric, which sounded even grander in Malayalam.
While fathers played sublimated sexual games with their nubile teenaged daughters, Poothana suckled young Krishna at her poisoned breast. Bhima disemboweled Dushasana and bathed Draupadi’s hair in his blood.
"Baleful" also means "threatening or foreshadowing evil or tragic developments"--while birds often represent omens of bad things to come, this definition would not fit the example sentence because 1) it is referring to things that have already happened and cannot be forgotten; 2) the bird is stuffed, most likely because it's dead, like the mounted bison head and Pappachi's moths.
Neither question nor answer was meant as anything more than a polite preamble to conversation. Both she and he knew that there are things that can be forgotten. And things that cannot—that sit on dusty shelves like stuffed birds with baleful, sideways-staring eyes.
And in a rush of snot and relief, it emerged. A little mauve bead in a glistening bed of slime. As proud as a pearl in an oyster. Children gathered around to admire it. The boy who was playing with the sign was scornful.
a person with a prejudiced belief in the superiority of his or her own kind
Rahel's repetition of Ammu's words is more humorous than hurtful, especially since Estha is not a chauvinist pig and they're in the middle of a conversation about love. When Ammu talks about male chauvinist pigs, she is disgusted because she is hurt by the chauvinistic rules of society. Despite working as hard as Chacko in the factory, she cannot inherit the property because she has no "locus standi" (legal standing).
“We don’t count,” Rahel said. “And anyway he might change. Ammu says.”
“How d’you mean? Change into what?” Sophie Mol asked.
“Into a Male Chauvinist Pig,” Rahel said.