It is possible to cause one answer circle to be empty

Kind of like this, if you would/could answer ABCDEF all the time.

```
[A][B][C][D][E][F]
[ ][A][B][C][D][E]
[F][A][B][C][D][E]
[F][A][B][C][D][E]
[F][A][B][C][D][E]
[F][A][B][C][D][E]
[F]
```

Probably caused by hitting spacebar at just the right moment after answering.