Final answer:
Fingernails are made of keratin and grow continuously, with the free margin extending beyond the finger or toe being the part that is usually clipped straight across for maintenance and to avoid ingrown nails.
Step-by-step explanation:
The statement that fingernails should be clipped straight across is generally recommended to prevent issues like ingrown nails. Fingernails and toenails are made up of specialized epidermal cells filled with keratin, which makes them tough and protective plates over the ends of fingers and toes. Nails are similar to claws in other animals, continuously growing from the nail beds by adding new cells. Older cells are pushed out, and the nail grows longer. The free margin of the nail is the part that extends beyond the finger or toe and is commonly trimmed to maintain neatness and prevent overgrowth.