Net Cash Flows from Selling the Bond and Investing
Investopedia has a good explanation of the term shorting which is what this is. In the simplest of terms, someone is borrowing the bond and selling it with the intent to replace the security and any dividends or coupons in the end. The idea is that if a bond is overvalued, one may be able to buy it back later for a cheaper price and pocket the difference. There are various rules about this including margin requirements to maintain since there is the risk of the security going up in price enough that someone may be forced into a buy to cover in the form of a margin call. If one can sell the bond at $960 now and then buy it back later for $952.38 then one could pocket the difference. Part of what you aren't seeing is what are other bonds doing in terms of their prices over time here. The key point here is that brokers may lend out securities and accrue interest on loaned securities for another point here.