Grenouille understands immediately that Monsieur Grimal only values Grenouille's life as long as it's useful to him, and Grenouille never resists him. The narrator states that Grenouille bottled up his defiance in a tick-like way. In the evenings, Grimal locks Grenouille in a closet to sleep on the floor, and during the day, Grenouille works as long as there's light. After a year Grenouille contracts anthrax, which is usually fatal, but Grenouille survives and is now immune to the disease. This makes him significantly more valuable as a worker, and he's finally allowed a bed and better food.
Here, even more so than Grenouille's other caregivers, Grimal sees Grenouille only as a means of profit. Grenouille is treated as little better than a domestic animal, and is forced even more than before to bottle up his humanity in order to stay alive. This makes the reader remember the narrator's earlier assertion that Grenouille chose life over love, and encourages consideration of how that idea works throughout the novel.
Beginning at age 12, Grimal allows Grenouille time to himself every week to explore the city. Grenouille "the tick" feels triumphant and alive, and experiences the urge to hunt for scents in the smelly city of Paris.
Note the language used to describe Grenouille. Even at this young age, he's "hunting" rather than exploring, making his actions seem predatory.