We form this Pi bond and that breaks the sigma bond. But as the sigma bond is broken, a pi bond is being formed between this carbon and this carbon. Now, as the pi bond is being broken, this pi bond breaks, and the two electrons in the pi bond end up on the nitrogen. And so the nitrogen in this Thiozol ring of the Thiamine pyrophosphate basically acts as an electron acceptor. It accepts those electrons, and it bears those two electrons in this intermediate molecule we call the activated glycoaldehyde. So we have the pi bond and the sigma bond between the carbon that came from this cellulose phyphosphate and this carbon here.