Hydrogen Cyanide (HCN) has the odor/taste of bitter almonds. Exposure to 10-30 ppm HCN in air can result in a metallic taste being reported.
Source: Clinical Environmental Health and Toxic Exposures, by John Burke Sullivan and Gary R. Kreiger, page 711.
HCN can be detected at levels from as low as 1ppm and the fatal dose, depending on the time of exposure, is much higher.
Some people can detect hydrogen cyanide by odor or taste sensation at a concentration of 1 ppm in air while most people can detect 5 ppm. OSHA has set 4.7 ppm as the maximum, average safe exposure limit for a 15 min period. [...] A small concentration of cyanide always exists in a person's body, and the body has a mechanism to continuously remove small amounts of cyanide.
Source: Riegel's Handbook of Industrial Chemistry by von Emil Raymond Riegel, James Albert Kent, page 1221.
Here is a toxicological overview.