The smoke of their torment (ho kapnos tou basanismou autōn). See Rev 9:5 for basanismos, only there it was a limited penalty, here it is “for ever and ever” (eis aiōnas aiōnōn, unto ages of ages). See also Rev 18:9; Rev 19:3; Rev 20:10.
They have no rest (ouk echousin anapausin). The very language used in Rev 4:8 of the four living creatures in praising God. “Those who desert Christ for Caesar will be the victims of a remorse that never dies or sleeps” (Swete). The rest of the verse repeats the solemn challenge of Rev 14:9.