Symbolism, Imagery, Allegory
Fizz powder is an old type of candy that Oskar can remember seeing around before World War Two. But in his present-day narrative, he realizes that it's almost impossible to find the stuff in any store after the war. In the novel, fizz powder represents sexual stimulation. When Maria and Oskar use it together, sparks fly.
"woodruff [fizz powder] nipped at her, woodruff penetrated her skin, woodruff excited her, gave her a feeling, a feeling, a feeling…" (22.19)
When he tries to bring up the subject of fizz powder with Maria later, though, Maria gets embarrassed and tells him not to talk about it. It's pretty clear that she also appreciates the sexual meaning of the fizz powder and feels ashamed about it. There's also the juxtaposition of something childish—candy—with something grownup: sex. This adds to the impression that the sex between Oskar and Maria is seriously demented.