Slave Island - S1-E7
Factual error: When Professor X is calling Moira McTaggart in Scotland, the phone number he uses is shown to have only dialed the exit code of 011, followed by a fictional seven-digit number with a 555 prefix. Since he is calling from the United States, he would have to dial the country code (44) and area code for the right part of Scotland. Plus UK numbers at that time had at least 9 numbers. (00:08:20)