Continuity mistake: In the flashback, "Andi" is dead with her right arm on the last step in most shots (as she was the first time we saw the scene) or the one below (like when Blanc is crouching and curses saying "Sh*tballs." (01:45:20)
Other mistake: The way Helen and Blanc clash into each other during the blackout differs radically between the first time and the lengthy flashback; in the flashback she is calling his name, and he tells her "There's great danger." Neither happened the first time we saw the scene. (01:07:00 - 01:43:20)
Continuity mistake: In the argument between Birdie and Peg that Helen happened to record, Kate Hudson's hands are in a different position in her lap in the reverse shots when she says "There's no stopping it" and just after she admits "It's my secret phone." (01:37:25)
Continuity mistake: In their bathroom consultation, Blanc compliments Helen about the 'interesting stuff about Whiskey'; he is leaning on the sink, and then suddenly he's gesticulating with that same hand. (00:01:29)
Continuity mistake: Whiskey is walking with Helen towards the pool. When they are under a colonnade, the Taurus pendant shifted towards her left pectoral much more than it was in the previous shot. (01:26:50)
Character mistake: In the flashback, Blanc tells Helen that when Miles will pull him aside to explain his presence, that is when it will be her chance to 'snoop'. However, that piece of dialogue is just unnecessarily wrong since the whole distraction with Miles lasts just a few minutes, does not facilitate at all her snooping, and all the other guests are in their rooms just unpacking and hanging out. If anything, Miles keeping the other guests entertained and gathered together is what would facilitate her. (01:25:45)