I know holly is toxic to some animals, so to be on the safe side, please monitor closely and give your beardie activated charcoal and water to try to flush it out of his system faster. If he starts throwing up or acting sick, I'd get him to the vet.
I saw this quote from our vet moderator Drachie613 (Tracie) for an ingested millipede situation.
"You could make a detox greens slurry out of parsley, cilantro, mint, basil & oregano or
some activated charcoal just to clean out his system, if needed."