When the price of the coin goes above the peg, new coins are created. These are paid out to Basis Shareholders as a dividend. If they gain enough coins in this, or if this is a coordinated effort they can they then dump these coins on the market, pushing the value of the basis coin below peg. When the price of the Basis coin is now below peg, they can purchase the Basis Bond (which I believe is purchased with Basis coins), and then profit when the coin returns to peg and they can cash in their bond. It basically let’s them profit twice, first in selling the coins, and then in recouping the value that they pushed it below peg.