Tips for Mid-term?

Normally, I do not give tips for mid-term exam.
If I do, it will be a bonus, or an extra credit if you would see it that way.
Now that we have this place for everyone to get some extra credit, I thought I might throw some bonus here once in a while.
Here is how it work:
From now on, I will be thinking about the mid-term questions until the day we actually have our mid-term (next Monday). When I see something important, and if I am near a computer, I will post it here to remind you to look into that. I probably would not give you an exact answer, but I suppose a question would eventually lead you to an answer.
I suggest everyone would visit this blog regularly and post photos regularly.
But again, all this is extra credit, you do not have to do it if you think you do not need it.