In a Pb(Mg1/3Nb2/3)O-3-35 mol% PbTiO3 (PMN-35PT) specimen with 5 mol% excess PbO, the pores trapped inside grains by heat treatment in a double cycle at 1150degreesC have revealed the coarsening pattern of the grains. Using this technique, the coarsening process of abnormal large grains with typical characteristics of penetration twins could be determined. The results suggest that two-dimensional nucleation and lateral growth enhanced at the reentrant edges are the cause of zigzag-shaped Sigma3 incoherent twin boundaries.