A Formation of pockets, explained by a passive front model, is controlled by breaking a vibrating air/methane flame at its top. Three types of pockets were observed droplet-shaped, spade-shaped and string-shaped. Using a near stoichiometric mixture, droplet-shaped pockets were quantified at 0.355 atm. From either their hydraulic diameter, or their axisymmetrical volume and area, global quantities such as stretch K, burning velocity S-d and curvature Co are obtained. S-d, at least twice the laminar burning speed S-L, reaches a maximum ranging from 3.5 S-L, to 6.4 S-L. K is correctly expressed by the product -S-d Co; from Poinsot et al. correlation connecting burning velocity to high curvature and strain, global relations written between S-d and K, and S-d and Co on the other hand, concur with data. A minimum experimental diameter at the final stage of combustion is found: its value is consistent with that of minimum diameter given by Poinsot et al.