"That animal is not dangerous."
Translation:Εκείνο το ζώο δεν είναι επικίνδυνο.
Stick with αυτό = this and εκείνο = that. Unlike in English, where 'that' is very common and often replaces 'this', εκείνο is not used as much as αυτό in comparison: it is used only to denote something not in close proximity specifically. In short, they are not interchangeable, not in real life, not in Duolingo. :)