A big budget doesn't always guarantee a perfect movie -- especially when special effects are involved.

Some of the biggest sci-fi movies of the past four decades are littered with plot holes, continuity errors, and, in some cases, blatant gaffes. For all you purists out there, here's a roundup of some of the sci-fi genre's most noticeable movie mistakes.

As usual, all photos are courtesy of MovieMistakes.com.sci-fi movie mistakes