How might I go about flagging a post or comment containing certain keywords? I have nodes coming in via FeedAPI and direct user submission, and I've got comments. A client requires me to check incoming nodes against a watch list of keywords. The posts and comments don't need to be blocked, because the watch list is fairly expansive (~1000 words but many are very context dependent). Rather, I need to be able to check the contents of a post or comment against the list and set a flag that triggers a notification to a moderator, who will manually review the content.

Is there a module that can help me with this? Barring a module, I could use a few clues to get me started on this, e.g. 

"To check the content on a newly published node or comment, you could do these things."

"To flag based on a hit, you could do this thing."
Look at hook_node_xyz (d7) or hook_nodeapi (d6) to add code after node save or update.