I was reading around on another dog forum and found a poster who suggested that the small hole in the top of kongs was to prevent the dog accidentally creating a vacuum seal through over zealous licking, thus getting it's tongue sealed into the kong . The suggestion was that when you are stuffing kongs you should put a pencil down through the middle so that the small hole remains open, and stuff around the pencil. To be honest I don't see how a dog could reasonably get it's tongue lodged in a kong via a vacuum effect, even if the small hole is closed over. It seems that at minimum it would require a small kong and a dog with a large tongue (i.e the wrong size kong). But even then, since dog's don't breathe through their mouths when they're eating it seems unlikely that a vacuum will occur via inhalation (in the same way that a human can stick a mug to their face if they inhale with it over their mouth). The only other option is that the vacuum is crated via very forceful licking, which seems a bit unfeasible? Has anyone actually witnessed a dog get it's tongue stuck in a kong through accidentally creating a vacuum? For what it's worth, I always assumed the small hole in a kong was for easy-cleaning.