You have a strand of hair from a crime scene but can’t tell if it is from an intruder or the family dog. if the hair otherwise looks similar on initial examination, you’d want to examine the: medulla nucleus root follicle

i took this class the answer is medulla because investigators may look for the presence or absence of a medulla, which is a set of cells that runs through a hair. The medulla is typically different depending on which species the hair came from. This is one way to distinguish between animal and human hair.

thinking it would be physical characteristics

there are so many examples for that in different areas, like biology experiment carried out in our lab recently.

here's one link: