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It's unlikely he swallowed a lot of plastic but he may have it in his pouches. The best thing is to put him in the cage then keep checking through his stuff to see if it appears.
Often they will chew it up or pouch it then once they feel safe it will come out again.
Feed veg like brocolli to keep his tummy moving well and if he shows any signs of being unwell like bloating or constipation then see the vet right away.