Martin Schneider writes:

As Pollux noted recently—and our friend Ben Bass posted too—there is a mind-blowing trick in the special four-Eustace 85th anniversary cover of last month. If you place the four covers in the proper two-by-two configuration, the outlines of the original classic Eustace cover can be discerned.

Now we have Adam Kempa's excellent slider application, which allows you to find it without spreading (multiple copies of) the issue all over your living room floor.

I am endlessly impressed by such cleverness! Françoise Mouly, hats off to you! (A top hat, of course.)