Less is more

Methyl mercaptan may be one of the worst smells we encounter in normal life but it gets worse with their selenium versions. Selenium is similar to sulfur in a chemical way but if you replace sulfur with it the smell INTENSIFIES DRAMATICALLY.
Most chemicals come to a point where it's enough to kill you and selenium is no exception. A single dose of 50mg is enough to end your life. Although it doesn't take much to kill us, it is still vital to our existence; we only need it in microgram quantities.
We store most of it in our skeleton but the places where the highest levels of selenium are other than that is in kidneys, hair, and testicles.
This element is also more rare than silver!