The concern of non-chametz food items coming in contact with something that will become chametz. For example, water used by a baker can easily contribute to leavening. Which connects to methods of cooking and what is acceptable as roasting. What about the hot springs of Tiberias? When cooking isn't quite cooking, roasting over a fire is quite specific. Also, what happens if the korban Pesach is not cooked fully? If one eats it anyway? The Gemara lists the sets of lashes that one would incur in various scenarios.