1. void gameOver() {
2.   //Play explosion and display game over screen if you lose
3.   if (currentLevel == 9) {
4.     pirateLaugh.rewind();
5.     pirateLaugh.play();
6.   }
7.   explosion.rewind();
8.   explosion.play();
9.   track1.pause();
10.   track2.pause();
11.   track3.pause();
12.   track4.pause();
13.   image(imgGameOver, 0, 0);
14.   if (keyPressed) {
15.     if (key == ' ') {
16.       currentLevel = 0;
17.       lives = 25;
18.       fuel = 0;
19.       score = 0;
20.       noUpDown = false;
21.       noLeftRight = false;
22.       setup();
23.     }
24.   }
25. }

So if you lose while on the boss level he laughs at you but the file still doesn't play properly.

1. void gameOver() {
2.   //Play explosion and display game over screen if you lose
3.   if (!gameOver) {
4.   if (currentLevel == 9) {
5.     pirateLaugh.rewind();
6.     pirateLaugh.play();
7.   }
8.   explosion.rewind();
9.   explosion.play();
10.   track1.pause();
11.   track2.pause();
12.   track3.pause();
13.   track4.pause();
14.   image(imgGameOver, 0, 0);
15.   gameOver = true;
16.   }
17.  
18.   if (keyPressed) {
19.     if (key == ' ') {
20.       currentLevel = 0;
21.       lives = 25;
22.       fuel = 0;
23.       score = 0;
24.       noUpDown = false;
25.       noLeftRight = false;
26.       setup();
27.     }
28.   }
29. }

Thanks again.