The yellow article node is special because you can switch between three different symbols on it. The original symbol looks like text, but it really represents all kinds of content. The other two symbols are a film symbol and a link symbol. The film symbol is there for the occasions when you want to show your students that you have put a film in the article and nothing else. The same goes for the link symbol, if you have mainly used the article node to tell them about an external page and to link to it. You find the possibility to switch to a new symbol inside the article node, at the bottom.