My dog ingested kite string?!?

While I was in the shower my dog got in the garbage can and ate some kite string that was in it. He never usually gets in the garbage so I don't know why that string appealed to him so much but now I am really worried about his health. He seemed perfectly fine for a few hours but now he's sort of walking strange(this could just because he's older and I've just now noticed it) and panting a lot and just a few moments ago he got up and let out a sharp screeching yelp, presumably of pain. No one had even touched him in the slightest he just got up walked about a step and yelped. I am seriously worried. He ate quite a bit of that string and I know it could mess with his organs. He's eaten other strange things before(such as 2 whole chicken with the bones and many chicken wings, he's a rascal and always goes after the chicken). What should I do???