"Worst case scenario?" John considered it for a minute. "You mis-scribe a sigil or misspeak a word too badly to compensate, the spell comes to a screeching halt, the Watchtowers leave in a huff and you and Aziraphale wind up having to put him back together yourselves before he bleeds to death. Magically speaking, it's a protective spell; getting it to do anything else would take a complete overhaul. The worst it'd do to him is hide or protect him from somebody or something you didn't intend. If it backlashed, which is possible in theory, it'd likely have the same effect on you."

"Honestly though, I'd be less worried about any side effects than I would about Belial himself," he added, remembering vividly both the unexpected snog in the bar and the iron grip that had come within millimeters of crushing his windpipe. "I couldn't begin to predict what he'd do if something did go wrong. You may want to have restraints in place if you're that worried about it."