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Do not make him throw up. You will need to take him into the vet. Ribbon can cause all kinds of problems. It is a very hard thing for them to pass on their own safely. Ribbon can form obstructions if left on its own to pass through. It can also cause cuts and lacerations in the throat or digestive tract, which can cause bleeding. If you see any hanging out of the mouth or rectum, DO NOT pull it out. You have no idea what it may be wrapped around, and pulling it could cause dramatic damage.
This is just one of those situations that there is no way around not going to the vet.
I hope it turns out ok.
My first responsibility your pet's health and is insuring that I give safe advice. Please understand that. I can not advise you to induce vomiting in this situation. That is only needed for toxic ingestion like antifreeze or some kind or poison; not foreign objects.