International Air Dates:
Australia: July 9, 2008 on Ten. (edit) This is Diane Farr's last episode as Megan Reeves, as the actress did not renew her contract, opting instead to spend more time with her family. (edit) Music:

"Warning Sign" by Coldplay
(last few minutes of the episode.) (edit) This episode is rated: TV14-LV. (edit)

(Don drives off after being called to a case, leaving Charlie and Alan on the front steps)
Charlie: This is gonna be harder than I thought.
Alan: I think it's...to be continued. (edit) (David pulls the mask off the suspect, revealing a white male)
Fraley: Who is that?!
David: I don't know...doesn't look much like a Pakistani. (edit) Colby: Okay, if it wasn't you guys, who else does this sort of thing?
CIA Agent: The FBI. (edit) CIA Agent: (After being asked if they kidnapped the victims) Wasn't us. The CIA doesn't do this...not in this country. (edit) David: (To Charlie, about his analysis) Can it tell us where the boat's going? Or, you know, what the cell's planning?
Colby: That's probably asking a lot of a metaphor. (edit) (Charlie is explaining what kind of mathematical analysis he will be using to help on the case)
Colby: With a name like that, I don't even want to ask, Charlie. (edit) Charlie: (to Don) You and I have two very different world views, and that's fine. But now you're crossing into my world, and making assumptions about how people like me can or should work. (edit) Don: "He who gives up freedom for safety deserves neither."
Megan: Benjamin Franklin?
Don: No, actually I think it's a bumper sticker I saw. (edit) Larry: I have to confess, this whole business of rearranging DNA to suit human needs, I find very exciting; in this rather...life-threatening, world-ending sort of way. (edit)

In this episode, Megan resigns her position with the FBI to move to Washington to pursue her doctorate and a career in counseling. (edit) Opening Numb3rs:

783,350,200 ONLINE RESEARCH DOCUMENTS
41,000 GENE LOCI IN RICE
112 DESIGNER VIRUSES
2 KIDNAPPED MEN (edit)

While talking with his brother next to the koi pond, Charlie identifies one of the koi as an older fish named "Tombrello." Dr. Thomas Tombrello (PhD Rice University, 1961) is the Chair of the Division of Physics, Mathematics and Astronomy at California Technical Institute (CalTech), the real-world university upon which Numb3rs' CalSci is based. (edit) Don: All roads lead to Pakistan.

This is in reference to the common phrase, "All roads lead to Rome." (edit) Title: "When Worlds Collide"

This episode shares a title with both a song and a book. The song "When Worlds Collide" is by the group Powerman 5000, while the book by the same name was written by Edwin Balmer. (edit)