Maybe you'd rather not know. If you're curious, see what Brigid Prayson found when she teamed up with her doctor dad and put hotdogs under the microscope.
(A) Brand C. Low-magnification view of cross section showing scattered fragments of skeletal muscle. Many of the vacuoles stain for lipid. The amorphous eosinophilic material represents filler material. (B) Brand B. High-magnification appearance of skeletal muscle (meat) in cross section. Ghosts of subsarcolemmal nuclei are visible. (C) Brand B. High magnification of a band of connective tissue resembling a tendon. (D) Brand A. Fragment of bone tissue at high magnification.
(E) Brand B. Fragment of soft tissue containing several blood vessels at high magnification. (F) Brand G. Plant material used as a filler in many hotdogs at high magnification. (G) Brand C. Cross section of a peripheral nerve fascicle at high magnification. (H) Brand E. High-magnification appearance of a fragment of articular cartilage tissue.
(I) Brand D. High-magnification appearance showing marked lipid and fat highlighted on oil red O staining. (J) Brand D. Ultrastructural appearance of skeletal muscle showing still visible Z bands and discohesion of the myofilaments resulting in obscuring of the normal banding pattern of the sarcomere (original magnification ×22000).”
I don't know if Brigid Prayson, who was in high school in 2008, still eats hotdogs, but here's what the abstract of her paper, with co-authors James T. McMahon and Richard A. Prayson, says:
A variety of routine techniques in surgical pathology including routine light microscopy with hematoxylin-eosin-stained sections, special staining, immunohistochemistry, and electron microscopy were used to assess for meat content and for other recognizable components. [...]
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.