A company that couldn't get financing any other way could get financing by issuing fixed price convertible bonds. "Fixed price convertible" means the bond can be converted into shares (of the company), but at a fixed price - aka, regardless of the value of each individual share, you are promised fixed a dollar amount of them.
This means if the share price drops, you will be "made whole" by getting issued enough shares to match the fixed price.
It's called death spiral bond, because if/when the price of such a company drops, these convertible bonds will trigger, causing the amount of shares to increase (as they issue new shares), which in turn causes the price of the existing shares to drop, ad-infinitum. Often the owners of the shares would end up with nothing as the shares' value drops to zero (or the company recovers, and they do make some money).
Swap bonds with UST, and shares with Luna, and you get the above scenario.