Short answers, pulled from the story.
Knives appeared at least 2.5 million years ago, making them one of the earliest tools used by humanity. The evidence comes from the Oldowan tools. The word knife derives from the Old Norse knifr, meaning knife or dirk.
Knife blades have been made from wood, bone, and stone such as flint and obsidian, then copper, bronze, iron, steel, ceramic, and titanium. Modern options include carbon steel, stainless steel, high carbon stainless steel, laminated and Damascus steel, titanium, ceramic, and disposable plastic.
A modern knife includes the blade, the handle, the point used for piercing, and the edge running from point to heel. Other parts are the grind, the spine, the optional fuller and ricasso, the hilt or butt, and an optional lanyard.
A Linerlock is a folding knife with a side-spring lock that can be opened and closed with one hand without repositioning the knife, and it is self-adjusting for wear. It was invented by Michael Walker. The Compression Lock and Frame Lock are later variants, the Frame Lock invented by Chris Reeve for the Sebenza.
An automatic or switchblade knife opens from spring energy released by a button or lever in the handle, and is severely restricted in the UK and most American states. An assisted opening knife uses springs that propel the blade only after the user moves it past a certain angle, with the blade itself acting as the actuator.
A knife under the bed during childbirth is said to ease pain, and one in a cradle headboard to protect a baby. In Greece a black-handled knife under the pillow wards off nightmares, and giving a knife as a gift is believed to sever a relationship unless a coin is exchanged as payment. Anglo-Saxon burials included knives, and samurai used a tantō for ritual seppuku.
Every baptised Sikh must wear a kirpan, a ceremonial knife, as one of the five visible symbols of the Sikh faith known as the Kakars.