Exodus 12:9

12:9 Do not eat it raw or boiled in water, but roast it over the fire with its head, its legs, and its entrails.

Exodus 29:17

29:17 Then you are to cut the ram into pieces and wash the entrails and its legs and put them on its pieces and on its head

sn This ruling was to prevent their eating it just softened by the fire or partially roasted as differing customs might prescribe or allow.