Streak bonuses
Getting 3 card matches correct in a row will double your score. The same goes for 3 questions answered in a row with 6 points or more each.
Negative score
Each time you turn over 2 cards that does not match, you're deducted 3 points. This means that you can end up with a negative score. So, you don't want any streak bonuses while having a negative score as it will double your negative score.