Investigate

Investigate is a keyword action introduced in Shadows over Innistrad.

Description
To investigate, you put a Clue token onto the battlefield. Clues are colorless artifacts, which have the ability ", Sacrifice this artifact: Draw a card."

Investigate sometimes is triggered when specific things happen. For example, you get to investigate whenever a land enters the battlefield under your control or a nontoken creature you control dies. There is also a number of cards that trigger when a Clue is sacrificed. It makes the decision of when to sacrifice a Clue more interesting. You don't always do it as soon as possible.