首楞嚴義疏注經 8.530

8.530

怨習是因，鬼為蠱毒，旁受畜類蛇蝎是形。還生人道，雜乎庸類，即庸鄙之流，性麁率者。

The habit of resentment was their cause: as ghosts they were gu-poison spirits, and laterally undergoing an animal rebirth, snakes and scorpions were their forms. Returning to birth in the human destiny, they mingle with the base category—that is, the vulgar and vile sort whose nature is coarse and rash.