may act<br>
    as an effective barrier.</p>
  <p> There is a THUMP and a brilliant flash of light at the<br>
    entrance -- the Entity is homing in on them. Riker<br>
    draws his phaser.</p>
  <p> RIKER<br>
    Let's seal this entrance.</p>
  <p> He and Data fire at boulders above the cave opening;<br>
    they tumble down, blocking it. Beverly approaches.</p>
  <p> BEVERLY<br>
    I hope there's enough air in here.</p>
  <p> RIKER<br>
    There should be a ventilation<br>
    source somewh