 <p>Because you're not waiting for the mouse button to be released before you trigger your buttons.</p> <ul> <li>When <code>pause()</code> starts, it brings up two buttons.</li> <li>User moves mouse to <code>Main Menu</code>.</li> <li>User clicks mouse.</li> <li>As soon as the mouse button is depressed, <code>game_intro()</code> is called, which puts a <code>Quit</code> button in the same place.</li> <li>The mouse button is <em>still</em> depressed, so the game quits.</li> </ul>