I was cooking burgers in my new cast iron grill pan and noticed two tiny holes in the inside bottom of it. The only reason I could even see them was because they were bubbling. The grease got in them which caused the holes to bubble. They're small holes, but big enough that I could fit a toothpick in them. Is this ok/normal? Or does this mean the pan is defective and should be exchanged? If I saw something like this in any other pan I would probably take it back, but I'm not familiar with cast iron, so I don't know what's normal.