Why does Raul say lunch is a memory of indigestion?

When Raul's eating lunch in the school cafeteria, he can't help staring at Chankara. For one thing, her face is covered with fading bruises. Chankara's always vowed that she'd never end up like her sister, physically assaulted by a string of abusive boyfriends. Yet she's had her own experience of abuse. The previous night, Chankara's boyfriend had tried his luck, but she didn't want to take things any further. He still persisted, so she hit him right across the face; he hit her back, hence the bruising to her face.
The bruises have almost vanished, but their shadows still remain. While Raul's watching Chankara, he suddenly realizes that it's rude to stare, so he eats up his lunch quickly—way too quickly—before she catches him looking at her. That explains why lunch for Raul was a "memory of indigestion."