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We study the monopole ($\bar{B}^0_0$) and quadrupole ($\bar{B}^0_2$) momentsof the 21-cm bispectrum (BS) from EoR simulations and present results forsqueezed and stretched triangles. Both $\bar{B}^0_0$ and $\bar{B}^0_2$ arepositive at the early stage of EoR where the mean neutral hydrogen (HI) densityfraction $\bar{x}_{\rm HI} \approx 0.99$. 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 whichmark 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 intermediatescale. This marks the emergence of distinct ionized bubbles in the neutralbackground. $\bar{B}^0_2$ is relatively less affected by this transition, andit mostly remains positive even when $\bar{B}^0_0$ becomes negative. The secondsign flip, which affects both $\bar{B}^0_0$ and $\bar{B}^0_2$, occurs at thelate stage of EoR $(\bar{x}_{\rm HI} < 0.5)$. This marks a transition in thetopology of the HI distribution, after which we have distinct HI islands in anionized 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 inunder-dense regions.

The monopole and quadrupole moments of the Epoch of Reionization (EoR) 21-cm bispectrum