The main substances here are HBrO2 = Bromous Acid; Br-= Bromide ion; ferroin and its oxidized form - ferriin.
(upper part of the scheme) Bromous Acid is involved into an autocatalytic reaction, its amount increases exponentially with time, like in an explosion process. The other result of this process is the production of ferriin (oxidized form of ferroin). For an observer the latter process is seen as a change in color from red (ferroin's color) to blue (ferriin's color).
when the amount of ferriin becomes large, due to its interaction with organic components, ferriin starts to change back slowly to ferroin (physically this is just one electron transportation into a molecule), AND Bromide ions are produced during this reaction (lower part of the scheme).
Bromide is an effective inhibitor of the autocatalytic process. Because of Bromide, the production of Bromous Acid is stopped and its amount is reduced.
The active processes in the system is started at STEP-2 slow change of ferriin to ferroin (blue changes to red). With time the medium turns red, Bromide ions are binded, and the system is able to repeat the STEP-1.
The presented scheme is just a sketch of real processes occurring in the system. Nonetheless, it gives basic understanding of the dynamics and allows to locate the main substances involved into the reaction: Bromous Acid, Bromide ions and ferroin.
X-axis stands for time and Y-axis - concentrations. Digits in the right-hand part corresponds to the BZR steps described above. The main observation here, is that there are two different time scales, i.e. there are fast processes (time of order of Tfr), and slow processes (of order Tref, subscript "ref" means refractoriness).