When Gru grabs Edith while trying to get the girls to sleep, Agnes is shown hopping on her bed while she laughs out loud, the sound of her laughter continues to play briefly even after she stops laughing.
After Gru punches the shark, and as Vector takes off, we get an aerial shot of the area and Gru is in a solid circle wall, apart from the entrance gate. The pyramid is outside of the wall, with the only way to reach it being to go through the gateway and round. Moments later, Gru runs towards it crossing the island but would have had to cross the wall before running straight up the pyramid.
When Gru returns home from stealing coffee and a pastry from a coffee shop, he gets out of his vehicle and speaks with his neighbor. His hands are empty as he talks, and he immediately steps toward his house after the conversation. The pastry appears inside his house in the next scene where Gru is sitting in his living room.
When we first see Gru's unicorn book, there in a hole in it and he puts his nose through it to simulate the unicorn's horn. This means every page has to have a hole in it. He then opens the book to read it and there is only a hole in the front cover. He flips every page in the book and no other page has a hole in it.
When the Times Square JumboTron is scrolling its message, the lettering appears damaged as it scrolls and maintains the same damaged/inconsistent state throughout the screen width. As a JumboTron is composed of stationary lights, a burnt bulb will cause the characters to be whole/correct as they clear the burnt area. The damage should be stationary and not scroll with the letter.
When Mr. Perkins of the Evil Bank shows Victor Perkins (Vector) the screen capture from his video conference with Gru, the shot that he displays never happened. It displays the Shrink Ray and all three girls at the bottom of the image with Gru. During the actual scene, the only person in the screen with the Shrink Ray present is Gru. Additionally Edith is the only daughter whom we ever see come into view on Mr. Perkins' screen.
When Gru is reading the story about the Three Little Kitties, he turns the pages while keeping his fingers inside of the puppets. This would be impossible because of the way the holes in the other pages line up with his fingers as he turns them.