Short answers, pulled from the story.
The earliest evidence of a knife is a stone flake dated to at least 2.5 million years ago. These Oldowan tools were discovered in the archaeological record and represent the first time humanity shaped a rock into a cutting edge.
Modern knife blades are made from carbon steel, stainless steel, high carbon stainless steel, titanium, and ceramic. Carbon steel offers the best edge retention while stainless steel resists corrosion, and titanium provides a higher strength-to-weight ratio.
Michael Walker invented the liner lock mechanism for folding knives. This design uses a side-spring lock that allows the blade to be opened and closed with one hand and self-adjusts for wear over time.
Automatic or switchblade knives are severely restricted by law in the UK and most American states. The Restriction of Offensive Weapons Act 1959 in the UK prohibits the carrying of certain knives in public, and laws target the rapid deployment of blades.
Ancient cultures used knives in rituals such as placing a black-handled knife under a pillow to keep away nightmares in ancient Greece. Samurai warriors performed ritual suicide with a tantō, and all baptised Sikhs must wear a kirpan as one of the five visible symbols of the Sikh faith.