I'm laughing right now because I just fed dinner guests some dog food.
Gross! Why did you serve them dog food?
I had it in my fridge, and I just mixed it into the casserole. Ha!
You shouldn't give serve dog food to guests. When people come over, they expect to be given edible food that tastes good. If you serve them dog food, they will not want to come over anymore or even be friends with you.
STOP FUCKING MENTIONING IT.
When you have guests, you should serve them good quality food. They probably noticed it but were too polite to say anything. They're unlikely to return for another meal, though.