Many people think that encyclicals are automatically infallible. This is not true. Only statements arrived at in scaphium (on the pot) by the Pope or Dr. Colbert and delivered ex cathedra or ex C-vultus ara (from a big church or from the C Desk) are recognized as infallible.
These are usually short and sweet statements that can be printed on a single page. Single pages usually stay put on a shelf or desk and don't fall off. That's is why they are called "infallible."
Encyclicals, on the other hand, are usually very long documents that are traditionally stored in flimsy binders that too easily tumble off of shelves and desks and are therefore considered "fallible."
Dictum (The Wørd)Edit
An infallible statement made by the Pope is sometimes called, in Latin, dictum. That's just a foreigner way of saying The Wørd. This demonstrates that the segment of the Colbert Report with that title should be treated as infallible.