Watch the blue cones. These represent enemy vision. If you enter a cone, the "Alert" phase begins.
"-Rev 1-" implies a revision, a tweak to the initial release. Perhaps it was a bug fix, or maybe it was an update to reflect changes in the real world that the game developers wanted to mirror in their virtual espionage thriller. Metal Gear Solid -Spain- -Disc 1- -Rev 1-.chd
: The original game was released on two physical discs; this file contains only the first half of the game. Watch the blue cones