my kid's breath smells like cat food

I don't have to tell the parents out there, but did you know four year olds are aliens...particularly boys? This afternoon I was prepping dinner when I had to step over my young son just one time too many for convenience. I looked down and saw him sitting cross-legged in front of the mirrored oven door. I said to him, "Duncan, what are you doing?" "I'm having a snack, Mom". I then take a much better look, and he's got the aluminum cat food bowl between his legs and he's "chowing" down (pun intended). "DUNCAN!! You're eating CAT food!" I say as I quickly recall the nutrient label I last saw on a bag of kitty crunchies...(protien 18%, fat 22%, carbohydrates 60%--sounds pretty balanced to me)...I take a calming breath and continue, "Duncan, why are you eating the cat's food? What's he going to eat?" He puts another morsel into his mouth and reflects a bit. "I like it, mommy...the pink ones taste like gum". I stiffle a gag. He ignores me and adds, "and the green ones have chewy insides, they're my favorites".

I guess there's more than one way to get your kids to eat their veggies, but when he starts to cough up a fur ball, who do I call--a vet or a pediatrician???