When Father Brown and Sid are searching at the brewery, Father Brown's umbrella can be see hanging on the chair at the desk. When they rush out of the room to try to escape undetected, Father Brown leaves the umbrella shaking back and forth on the chair. In the next shot, as they're coming down the stairs, he is again holding the umbrella.
In Gabriel's office, Father Brown finds the book "A Silver Chalice" by Thomas Costain, but the text inside is actually from "The Long March" by Sun Shuyun.