Why do dogs eat there own 💩?!

I just had put my dog in his cage b4 going to the bathroom (I have to put him up or he'll chew my daughter's oxygen cords up so I put him in his cage until I get out and able to watch him running around He's still a pup just 3 months new of age. He gets feed morning noon and night with just the right amount of scoops his vet told us to give him 7am-1pm-7pm I feed him just an hour ago, my 3yr old comes tell me mommy puppy went potty in his cage so I said ok give mommy just a minute and I'll clean him..3min later I walk in the living room walking towards him and watch him start chewing his 💩💩!! I didn't know what to do or think but to quickly grab him and try to rinse his mouth out with the removable shower head in the shower! Is this normal? Maybe he's sick or something? Lol I just have never actually witnessed something so gross 🤢🤮 b4 🙈 he has access to water 24-7 and tons of toys. Hes a French bulldog