The Torsk Egg
entering new numbers reveals a joke that's not
when the silent service is safe, only one can be in the quiver
Dan'ni used the first two clues to discover the Torsk egg, which is something that looks like it belongs in Myst Mayhem, the April Fools 2000 joke by Cyan that in fact tipped off the existence of realMyst. A picture associated with this joke is here.
There are several places in realMyst where numbers can be entered; the one that works for this egg is the safe in the cabin on Myst Island. "Torsk" is another name for cod, but it is also a U.S. submarine, SS 423. Enter 4-2-3 into the safe combination.
The next step comes, I think, from the latest Spyder clue, "when the silent service is safe, only one can be in the quiver," although Dan'ni discovered it before the last clue! When the submarine number (silent service = naval submarines) has been entered into the safe, go to the columns near the stoneship model and push only the arrow column ("only one can be in the quiver.") The egg will appear. The egg actually works if other columns are pushed, but the arrow must be pushed.
What you then get is something that looks like this: