At https://phys.org/news/2019-10-astronomers-cyanide-gas-interstellar-2ibor… … which concerns comet Borisov, the newcomer currently making its way through the solar system. Data gathered by the William Herschel Telescope founhd it contains cyanide. It is therefore potentially dangerous to life on Earth – a killer. However, calculations of its future trajectory show it is not going to come anywhere in the vicinity of the Earth. Saved by the bell. However, that doesn't rule out cometary encounters in the past that may have caused cyanide to rain down upon Earth's atmosphere. Back in 1910 the Earth passed through the orbit of Halley's Comet and our atmosphere brushed against the tail of the comet. It is said to have contained cyanegic gas and yet we survived without a blemish it would seem. Earlier encounters with Halley's Comet may have been different, one might muse, but actual evidence of cyanide poisoning has not been discovered in various human remains (although it may be that it has not been looked for). Comets also contain other noxious chemicals – as well as harmless chemicals.