One and the same electron in a p orbital and taking part in a common π (pi) bond has two lobes visualized as connecting through the nucleus. There is however zero probability of finding an electron at the plane through the nucleus at right angles to the lobes.
Where has the electron gone? Is the electron tunneling through the nucleus as a virtual photon?

Ed./ Without altering the meaning of the original question it is more clearly stated as: How does the electron cross the nucleus.