According to Durst, the answer is meth.
Authorities arrested the 73-year-old Durst in New Orleans shortly after the series finale aired.
Whether or not his claim that his recorded admission is invalid due to meth use will stand up in court remains to be seen, but Durst's criminal history has been darkly charmed: after admitting to shooting, chopping up, and then dropping his neighbor into Galveston Bay when he was living in Texas, he was acquitted for acting in self-defense.
If the claims of meth abuse are true and the Durst-style belches were one of their side effects, then we suggest drug prevention campaigns get the word out ASAP.