4 yr old "Oral Fixation"

My son is 4 years old, almost 5. Recently he has swallowed a nickle, rocks, something off of the cat, and those are just the things that he's told us about. We have never had any of these issues with him as a baby or young toddler. He never had a pacifier, and gave up the bottle quickly. He's never displayed any sort of "Oral Fixations" in his life thus far. Whenever we ask him why he does it, he simply replies that "He doesn't know." He also says that "He doesn't want to but does anyway." Is this normal? It seems that disciplining him does nothing and we've tried to scare him saying he could end up in the hospital if he doesn't stop. What should we do?

[MImom0608]

It sounds like Pica to me. I would take him to the doctor and get him evaluated. Pica can cause problems because the individuals do not want to do what they do, it is a compulsion