I'll give you the middle of a word, and you'll try to guess the rest, one letter at a time. Every time you guess wrong, you'll lose a point. At zero points, you lose.
The secret word is chosen so that its middle is unique among commonly-known words (ignoring plural nouns and singular verbs). For instance, the middle OBC appears in the common word BOBCAT and no other common singular word (it also appears in the uncommon word MOBCAP, a kind of bonnet that nobody has heard of).
This means that, with perfect play, you'll never lose a point.
There is always at least one unknown letter at the start, and at least one at the end. So if you see a middle that starts with "non", you'll know it's not a word like "nonsense" — instead, it will have "non" somewhere in the middle.
You can guess letters at the start or end of the revealed section. Just click the corresponding yellow box. If you guess wrong, the letter you have selected will go into a red box. The letter might appear elsewhere in the word, but not at that location. (Indeed, there might be no letter at that location at all!).