How to select the first keywords?

In the latest google trends, I select two keyword:rare twins and i am sam.

Although rare twins is hot in July 25 but the rare twins is fit to curiosity of people and I think guy would still be interested in next days. It means the keyword I selected would not be outdate just after I select.

As for i am sam, I haven't understand.
So how, I can get why by google, which is the best teacher.