A surgical stapler can comprise an anvil comprising a staple pocket formed in a tissue contacting surface. The staple pocket can comprise a midline or centerline, a first forming cup, and a second forming cup. The first forming cup can comprise a first interior sidewall comprising a first vertical portion which is substantially perpendicular to the tissue contacting surface. The second forming cup can comprise a second interior sidewall comprising a second vertical portion which is substantially perpendicular to the tissue contacting surface. The first vertical portion and the second vertical portion can extend through the centerline, wherein the first interior sidewall and the second interior sidewall can comprise a trap for deforming a first staple leg of a staple to a first side of the centerline and for deforming a second staple leg of the staple to a second side of the centerline.