The Undelete Pill is a special item in World of Goo. It appears as a red pill labeled "undelete*", and exists in only one level, Deliverance, at the end of Chapter 4. The Undelete Pill is used in the Recycle Bin to reverse the deletion of years' worth of MOM's spam messages. With the millions of spam messages upon them, World of Goo Corporation explodes, one moment after a comedic computer terminal displays the message "new mail!"
The use of the Undelete Pill is to take back years of spam from the recycle bin in the Information Superhighway. The effect of the Undelete Pill is evidently very dangerous and irreversible.