A friend's dogs were playing like that and one got its lower jaw snagged under the collar of the other, they twisted and it became a tourniquet. She was home and was unable to release it, but she had the presence of mind to grab a kitchen knife and cut the collar before the dog was fatally choked (not without its own risks to her and both dogs considering the urgency and violent stress and movement in the situation).

Another even more gruesome thought -- if you have a paper shredder make SURE it is not in reach of your dog. Dogs will lick anything with a scent that interests them, and as unlikely as it seems you can't take that chance. (I read of one instance).