Off-the-shelf computer games typically have a button that allow the player to "replay" or "hear again." Lexercise games don't have this option. Here's why:
To be fluent a reader must be right on the first try. One of the purposes of Isolator is to improve the rapid (fluent) processing of speech sounds in words. But, if the player could succeed by listening to a word over and over there would not be a strong incentive to be right on the first try. Allowing a player to repeat a target word would also disrupt the tracking of accuracy data. What we really need to know is: How often the player is accurate on the first try.
Isolator does give the player a second and a third try (for fewer points), and on these second and third tries the word is spoken at a normal rate but in clear speech, which provides a stronger, clearer speech model of the spoken word. (Although the player is not aware of it, the second and third responses are not counted for accuracy data. To be counted as "accurate" the player has to be correct on the first try.)
You might wonder why the words aren't just spoken more slowly for the second and third tries. Speech science tells us that there is no way to slow up the speech sounds in words without also distorting them. So, second or third tries with slowed up words is not an option.
Here is an article about how the Lexercise Games use clear speech to help the player succeed on the second and third tries.