Okay kiddo, let me explain what dimethyl selenide is.
You know how everything around us is made up of tiny things called atoms? Well, dimethyl selenide is made up of three different atoms - carbon, hydrogen, and selenium.
But what's interesting about dimethyl selenide is that it has a special smell - kind of like garlic or rotten eggs. It's not a pleasant smell, but scientists use it as a way to detect selenium in places like soil or water.
Selenium is an important element for our bodies in small amounts, but too much of it can be harmful. So, scientists use dimethyl selenide to figure out how much selenium is around us and if it's safe or not.
So, that's what dimethyl selenide is - a stinky chemical that helps scientists keep us safe!