Keith tells Karen if she gets scared at night to knock once on her bedroom wall and he'll knock back twice to let her know he's there. That night, she gets scared and knocks twice instead of once and someone (supposedly Keith) knocks back once instead of twice.
Dr. Prell and Karl talk about how the code of the Voltaire demands no body bruises and how a victim must be scared to death. Later, at the big breakfast, they go around toasting past party hosts, bringing up highlights which include an avalanche and auto crashes. Wouldn't those two scenarios inflict body bruises?
Spencer St. Claire's flashback, which is supposed to be set during a snowstorm appears to be filmed in the middle of fall. The color tint, brightness and contrast are tuned up to a degree where everything appears white, however, you can clearly see Spencer crawling through leaves instead of snow.