Originally posted by CliffLandinExactly, but only in the move directly after the b pawn's first move of b2-b4.
If I read this correctly, if pawn1's opening move is two spaces placing it on the square next to an opposing pawn, pawn2, pawn2 can move to the square that pawn1 moved over, capturing pawn1. Sorry that I don't know real chess lingo, but let me give it a shot.
b2-b4, c4-b3 capturing b4
D