The scratch wounds on Lynn's face change noticeably between the time of her attack and the times we see her body afterwards.
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.
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?
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.
When the group arrives at the house and everyone leaves the van, the last person to leave the van closes the sliding door and pats it as though it was closed successfully when it is clear that it did not fully close.