the engine. The rear wheels are coupled to the rudder to provide steering during taxiing. To maintain balance while taxiing and take-off, two auxiliary wheels called "pogos" are attached under the wings. These fit into sockets underneath each wing at about mid-span and fall off at takeoff. To protect the wings during landing, each wingtip has a titanium skid. After the U-2 comes to a halt, the ground crew re-installs the pogos, then the aircraft taxis to parking. Because of the high operating altitude and the cockpit's partial pressurization, equivalent to pressure altitude, the pilot wears a partially pressurized space suit, which delivers the pilot's oxygen supply and provides emergency protection in case cabin pressure is lost. While pilots can drink water and eat various liquid foods in squeezable containers through a self-sealing hole in the face mask, they typically lose up to 5% of their body mass on an eight-hour mission. Most pilots chose not to take with them the suicide pill offered before missions. If put in the mouth and bitten, the "L-pill"—containing liquid potassium cyanide—would cause death in 10–15 seconds. After a pilot almost accidentally ingested an L-pill instead of candy during a December 1956 flight, the suicide pills were put into boxes to avoid confusion. When in 1960 the CIA realized that a pill breaking inside the cockpit would kill the pilot, it destroyed the L-pills, and as a replacement, its Technical Services Division developed a needle poisoned with a powerful shellfish toxin and hidden in a silver dollar. Only one was made because the agency decided if any pilot needed to use it the program would probably be canceled. Like the suicide pill, not all pilots carried the coin, and Knutson did not know of any that intended to commit suicide; he carried it as an escape tool. To decrease the risk of developing decompression sickness, pilots breathe 100% oxygen for an hour prior to taking off to remove nitrogen from the blood. A portable oxygen supply is used during transport to the aircraft. Since 2001, more than a dozen pilots have reportedly suffered the effects of decompression sickness, including permanent brain damage in nine cases; initial symptoms include disorientation and becoming unable to read. Factors increasing the risk of illness since 2001 include longer mission durations and more cockpit activity. Conventional reconnaissance missions would limit pilot duties to maintaining flight paths for camera photography.