I've just noticed a bug/glitch/inconsistency in the way that the 'Swordfish' routine is executed at the end of the Final Barrier.
When Willy enters the portal (unless you're playing in Cheat Mode, of course), his sprite appears above the portal which displays the Swordfish icon. There is also a command which overwrites the attributes of the two cells underneath the portal, in order to disguise Willy's feet (so that he doesn't appear to be in two places at once!)
However, once the points start to be ratcheted up as the remaining air supply is counted down, Willy's feet are still visible (in blue INK on black PAPER), because the pixel display for those two cells isn't wiped, only the white INK attribute.
Incidentally, the green PAPER attribute of the cells occupied by Willy's lower half when he is drawn above the Swordfish would possibly look a bit better if cyan PAPER was used (as is the case for the upper half of his sprite at that point).