Knife with extensible blade

A knife having an extensible blade, the knife comprising:

• a handle having:
• a front end, a back end, an exterior, and a handle cavity that is located inside the handle, wherein the handle cavity is open at least at the front end of the handle, the handle cavity defining:
• a guiding groove extending from a first location toward the back end of the handle to a second location toward the front end of the handle, wherein the guiding groove comprises a stop toward the front end of the handle;
• and
• a pull-out groove that extends along a length of the handle and that is open at least at the front end of the handle;
• and
• a blade with a point, a blunt end, a guiding member that corresponds in shape, size, and position with the guiding groove;
• a connecting member on the blade that corresponds in position with the pull-out groove, wherein the connecting member is placed closer to the point of the blade than is the guiding member with respect to the point of the blade;
• a pulling element that is equipped at one end with a joint member, wherein the joint member is equipped with a connecting element that is selectively connectable with the connecting member of the blade, wherein the joint member further corresponds in shape, size, and position with the pull-out groove, and wherein the pulling element is configured to extend through the pull-out groove out from the handle when the blade is in a retracted position;
• a locking bed that is parallel to the length of the handle, the locking bed having an open receiving end that is perpendicular to the length of the handle;
• and
• a rotary controller that comprises a rod-shaped, rotary-pivoted element that lies in the locking bed, and a manipulator that lies at a right angle to the rod-shaped, rotary-pivoted element, wherein the manipulator extends beyond the handle for selectively locking and unlocking the blade in the retracted position.