The affix ḍāc comes after the word śūla followed by kṛ 'to make' when the sense is that of roasting.,
Thus शूले पचति = शूला करोति मांसम् \he roasts the meat on a spit\. Why do we say \when meaning to roast\ ? Observe शूलं करोति कदन्नम् \the bad food causes colic\.,