error Cannot read property 'add' of undefined

I'm a little bit stuck with my excersice. I know there are many questions about this error, but I couldn't find my answer. I hope you can help!

This is my code:

let mijnDivs = document.querySelectorAll('div')
let i = 0;
let woorden = ["kip", "konijn", "paard", "varken", "gerbil", "hamster", 
"rat", "zeeduivel", "narwal", "orka"];
while (i< mijnDivs.length) {
i++;
 }
setInterval(() => {
twoSec();
}, 2000);

function randomNumber(min, max) {
min = Math.ceil(min);
max = Math.floor(max);
return Math.floor(Math.random() * (max - min + 1)) + min;
}
function twoSec(woorden) {
let randomWords = this.classList.add(woorden[randomNumber(0,9)])
}