Janis: Your pan where you fried the cutlets is a mess!
Janis: It'll take some soap and water to clean this!
Arlo: OK, OK, but let me.
Janis: Granny would be amazed to learn women can no longer be trusted with cast-iron cookware!
One doesn’t scrub cast iron pans with soap and water; one seasons them, gently, with oil. Arlo seems to know about it, but Janis does not, so he’s going to do it (sort of) himself. If she doesn’t know by now, she never will.