When Mabel shows Dipper her hickey, it's on her right cheek. But in her flashback of how she really got it -- kissing a leaf blower in vacuum mode -- the leaf blower is stuck directly over her mouth.
At 5:26 when Dipper is reading the book he found in the forest, the written words in the book do not match what Dipper says. The book shows the word "researching" while Dipper says "studying".