Claire tells the audience that she diagnosed Colum 'after a week's observation', yet she was scheduled to leave five days after she first met him and the statement occurs well before then.
Claire refers to Colum's men as 'thugs', and Colum apparently understands the term and is unfazed by it. The term originally referred to gangs of robbers in India and came into English usage during the era of British rule, which had not yet begun in 1743.
When Mrs. Fitz wakes Clare up when she gets to Castle Leoch she says Clare slept till 5, but it was full light. At 5 am in October it would be pitch black and not full light.
While tending Jamie's wounds at the castle, Claire sticks her hand, with a rag in it, into boiling water.
Claire claims that Henri de Toulouse-Lautrec was 38 years old when he died. In actuality, he died on September 9, 1901 at the age of 36.