Marco Polo - S1-E4
Factual error: The story is set in 1289, when Marco Polo was anxious to leave China against Kublai Khan's wishes, so what's Polo doing on the Pamir Plateau?
It Crawled Out of the Woodwork - S1-E11
Factual error: When the energy monster kills his entire research staff by stopping their hearts, Dr. Block brings them all back to life (with their minds and personalities intact) by installing pacemakers. But when the heart stops functioning, brain death occurs within minutes. For this to work, he'd not only have to operate on several people simultaneously, he'd also have to be the fastest heart surgeon on Earth. (00:40:00)