About Searching Bodies and All Headers

First, you need to be using Build 2.9.11 or later. Next, you need to use a BODY condition (not a "Header Contains" condition). A BODY condition will search the entire article source (what you see when you turn on All Headers and View Article Source).
Note that in the Search Window (only), headers and bodies are separated, and you can Look in Header or Look in Body. In this case Look in Header refers to the full headers and behaves the same as searching Bodies (i.e., unless you limit Body and Header searches to search Local articles only, Gravity starts fetching the article bodies from the server, and does not save them after the search).
Do not confuse this with a  "HEADER Contains" condition in filters, rules, and scoring. These only work on the From, Subject, Date, and Message-ID headers (in all Gravity versions) and do not require article bodies.
In order for a BODY condition to work immediately, you must set the Newsgroup to store article bodies. Otherwise, the rule or score will not act until the body is available (usually when you read it, which may be too late depending on your intent).