  We study the monopole ($\bar{B}^0_0$) and quadrupole ($\bar{B}^0_2$) moments
of the 21-cm bispectrum (BS) from EoR simulations and present results for
squeezed and stretched triangles. Both $\bar{B}^0_0$ and $\bar{B}^0_2$ are
positive at the early stage of EoR where the mean neutral hydrogen (HI) density
fraction $\bar{x}_{\rm HI} \approx 0.99$. The subsequent evolution of
$\bar{B}^0_0$ and $\bar{B}^0_2$ at large and intermediate scales $(k=0.29$ and
$0.56 \, {\rm Mpc}^{-1}$ respectively) is punctuated by two sign changes which
mark transitions in the HI distribution. The first sign flip where
$\bar{B}^0_0$ becomes negative occurs in the intermediate stages of EoR
$(\bar{x}_{\rm HI} > 0.5)$, at large scale first followed by the intermediate
scale. This marks the emergence of distinct ionized bubbles in the neutral
background. $\bar{B}^0_2$ is relatively less affected by this transition, and
it mostly remains positive even when $\bar{B}^0_0$ becomes negative. The second
sign flip, which affects both $\bar{B}^0_0$ and $\bar{B}^0_2$, occurs at the
late stage of EoR $(\bar{x}_{\rm HI} < 0.5)$. This marks a transition in the
topology of the HI distribution, after which we have distinct HI islands in an
ionized background. This causes $\bar{B}^0_0$ to become positive. The negative
$\bar{B}^0_2$ is a definite indication that the HI islands survive only in
under-dense regions.
