I've figured that much. How come?

What do you mean by that exactly? Anyway, I had the same issue when I did this kata with loops (though every test case I used in repl.it worked, so I'm not sure what they're even passing in as an argument that's making it break) and it failed here. But then I did forEach and that worked. Any insights as to why?

I think the problem isn't clearly worded. Could you possibly clarify it? Others seem to have expressed similar concerns.

Thanks!