Tool - 10,000 days hidden stuff
 

Well not really hidden but an easter egg for sure:

Open up your favourite media player, and make a playlist with:
Viginti Tres
Wings For Marie (Pt 1)
Now, open up either a second media player, or pop the CD into your stereo, and get the 4th track ready:
10,000 Days (Wings Pt 2)
Make sure you start them both playing at the same time. The two will synch up perfectly. The singing at the end also synchs up completely if you played them at the right time.
Tool meant these tracks to synch. They wanted to make an epic flowing song like an 8-peice band as a tribute to Maynard's mother's passing. If you look at the track times, "10,000 Days" is 11 mins and 13 seconds long. When you add the track times of "Viginti Tres" and "Wings for Marie", they add up to 11:13 as well. Also, "Viginti Tres" means the number 23 in Latin, and 23 is the number of synchronicity.