The following text was taken from the 'Roadside Picnic' Wikipedia page before it was removed on the grounds that it was "superfluous trivia". (13 May 2012)

Artifacts left by Visitors in the Zones

The artifacts left behind by the Visitors can be broken down into four categories:

(1) Objects beneficial to humans, yet whose original purpose, how precisely they work or how to manufacture them is not understood. The 'So-So' and 'Bracelets' are among the artifacts that fall into this category.

(2) Objects whose functionality, original purpose or how to use them to benefit humans can not yet be understood. The 'Black Sprays' and 'Needles' are among the artifacts that fall into this category.

(3) Objects that are unique. Their existence is passed along as legends by Stalkers; were never seen by scientists, whose functionality is so dangerous and so far beyond human comprehension that they are better off left undisturbed. The 'Golden Sphere' and the 'Jolly Ghost' are among the artifacts that fall into this category.

(4) Not object but effects on people who were present inside the Zones during the Visitation. Humans who survived the Visitation without going blind (apparently from a loud noise) or infected by the plague caused unexplained problems if they emigrated away. A barber who survived the Visitation emigrated to a far off city and within a year 90% of his customers died in mysterious circumstances as well as a number of natural disasters foreign to the area (typhoons, tornadoes) hit his city. Even people who were never present during the Visitation but frequently visit the Zone are changed somehow, for example by having mutated children or by having duplicates of their dead relatives return to their homes.

An entire economy has developed around the Zone in the trade of items obtained from the Zone by Stalkers. The only legal buyer of artifacts is the Institute for Extraterrestrial Cultures, but a large black market has also evolved. Stalkers will seek to gain the best price of artifacts while avoiding the police who enforce strict laws against the black market. The functioning of this market and the relative prices Stalkers are paid for different artifacts plays a key role in the plot. The novel also provides some idea for the relative markup of prices as items move from Stalkers to external markets like Europe, where the highest prices can be obtained, usually about five times what the Stalker was paid. Prices are often given in the novel but never in currency, just numbers. Other times prices are given in relative sums, for example a Stalker is paid two months salary as a bonus for getting a certain 'full empty' early in the novel. So the price of a battery paid to a Stalker is given as 20.



There are also a number of unexplained events or patterns associated with the Zone. Some relate to the Visitation itself. For example on the night of the Visitation many people were blinded, they all reported being blinded by the sound of a thunderbolt. But no one person who was not blinded heard the thunderbolt. Also the Stalker Red reports that people new to the Zone suddenly lose the ability to control their own speaking in the Zone, though this may be nerves or related to the Zone itself.