Continuity mistake: In one of the first family scenes, the youngest daughter shows she has lost a tooth. The next shot, the tooth is back in her mouth. (00:15:10)
Continuity mistake: The taxi ride to the planetarium begins in a Ford Crown Victoria but ends in a Chevy Caprice. (00:36:02)
Continuity mistake: When Prot takes his sunglasses off for his "return" (because he would supposedly no longer need them due to the lower light levels on K-Pax), he places them on the nightstand upside-down, with the earpiece flush to the table. Two subsequent shots (including an elaborate effects shot) show the sunglasses right-side-up. (01:48:45 - 01:53:30)
Continuity mistake: The bowl of green jello that Doris throws at the warden lands the right way up, but in the next shot it is upside down. (00:21:00)
Continuity mistake: When the woman who never leaves her room is seated at the table with some other patients, she's talking to the doctor and closes her hand fan. The very next scene shows the fan open again.