It's common wisdom that you don't want to know how sausage is made. Well, for good reasons, actually.

Back in 2008, then high schooler Brigid Prayson teamed up with her doctor dad to do histological and electron microscopy studies on various brands of hot dogs to see what's exactly in them:

Meat content determined by microscopic cross-section analysis ranged from 2.9% to 21.2% (median, 5.7%). The cost per hotdog ($0.12-$0.42) roughly correlated with meat content. A variety of tissues were observed besides skeletal muscle including bone (n = 8), collagen (n = 8), blood vessels (n = 8), plant material (n = 8), peripheral nerve (n = 7), adipose (n = 5), cartilage (n = 4), and skin (n = 1). Glial fibrillary acidic protein immunostaining was not observed in any of the hotdogs. Lipid content on oil red O staining was graded as moderate in 3 hotdogs and marked in 5 hotdogs. Electron microscopy showed recognizable skeletal muscle with evidence of degenerative changes. In conclusion, hotdog ingredient labels are misleading; most brands are more than 50% water by weight. The amount of meat (skeletal muscle) in most brands comprised less than 10% of the cross-sectional surface area. More expensive brands generally had more meat. All hotdogs contained other tissue types (bone and cartilage) not related to skeletal muscle; brain tissue was not present.

Science, must you be such a buzz kill? Link