There is no real "secret" to Explore. That's the big secret.
Ever come across a photo with dozens if not hundreds of comments, and they all have these little blinky "Best of Sparkly Award" graphics in them? "Diamond in the Rough!". "Flaming Sword of Awesome!!" etc etc. Well the reason for that is many people are members of Flickr groups that enforce strict "commenting" rules. To post to the group, you have to first comment on some other photos in the group, or favorite them, or give them award blinkies. It's an artificial "game" of false attention, almost all geared towards one thing: getting their photos on Explore.
What is Explore?
"Explore" is basically Flickr's front page, an introductory collection of ever-changing photos to show people the kinds of things inside the site. Each day Explore displays 500 images, but those images are constantly changing, as new photos are uploaded throughout the day.
To some people, Explore is the ultimate beauty contest. It's the pinnacle of Flickr, the achievement of achievements. They fret and conspire and worry, and actually get angry and frustrated, when their perfectly fine photos, never "get into" Explore.
Except it's basically random. No matter how artificially "interesting" you try to make your photos (Explore photos are selected via Flickr's "Interestingness Algorithm", affectionately known as the "Magic Donkey"), Explore is still only 500+ images each day. And each day on Flickr, there are more than five thousand photos uploaded each minute. That's each minute.
So to help these poor souls, to shed some light on the mysteries and myths of Explore, a Group was formed. "The Secrets of Explore". A clearinghouse of info to clear up the nonsense, to spread some fact jelly over fiction bread.
And of course, it has its very own blinky graphic. This artwork might go blinky for the cause as well, but it's also an homage, a bit of a congrats and thank you, to the fine Flickr volunteers who risk their sanity, to tell TruthToExplore(tm). Why pandas, you ask? Why pandas vomiting rainbows?
That's a whole other secret.
larger one here.