After Alex and Sara finish their first date and she gets into the taxi, Alex's shirt gets caught in the taxi door and it rips; it doesn't just slip off of him. When they meet again at the fish restaurant, Sara returns Alex's shirt (it appears to have been dry cleaned) and it is not ripped.
When Hitch suffers from food allergy the right side of his face and his right ear are shown to swell up. This is shown also in the pharmacy scene but when they get outside and he is drinking from the medicine bottle with a straw his swollen ear and reduced puffy face are on his left side.
The bar scene where Hitch is talking to his friend while playing pool, a girl in a white top passes behind him and then the next shot she passes by him again.
When Albert kisses Alex, a large pimple appears and disappears on Alex's right cheek in various shots.
When Sara and friend are in the store shopping, Sara has her purse hanging from her shoulder. The buckle on the purse strap changes positions from the front to the back.
When Sarah is trying to drive the manual transmission car near the end of the film, a shot is shown of her pushing down the gas pedal and the car taking off. However, her left foot is not on the clutch at all. With a manual transmission, the car would have stalled without having the clutch pushed in and then gradually releasing it while pressing the accelerator.
When Hitch's shirt gets caught on Sara's taxi, Sara is holding onto the shirt as the taxi drives off.
When Hitch is talking to Sara at the end of the movie, one of the extras walks by twice, in the same direction (upper-left corner).
At the end of the movie where Hitch is giving his speech in the middle of the street. Around 1:49:52 in the upper right corner you can see a red tour bus, and the people on top clearly get up abruptly and start pointing at the camera.
In the newspaper article of Allegra's break-up that Albert reads in the beginning of the movie most of the visible text is repeated.
After Hitch's food allergy, he brings home an assortment of coffee and tea for Sara and himself at her apartment. When he hands her the tea, and when they are each drinking their own coffee/tea, it is obvious that the coffee cups have nothing in them. They clearly hold and drink out of empty cups. When he opens the plastic top, it makes a hollow sound - and is obviously empty.
At the very end of the film, during the dance sequence, the onlookers are clapping completely out of synch with the hand claps heard on the soundtrack.
Throughout the walkie talkie exchange between Hitch and Sara both characters fail multiple times to key their mic yet the squawk sound still plays.
After Albert kisses Alex, Alex walks down the set of stairs and makes a disgusted sound, but his lips don't move.
When Sara and her friend are dining in the restaurant Rice to Riches, you can clearly hear the clink of cutlery against dishes in the background. However, all the dish ware in Rice to Riches is plastic, and thus would not make such a sound. You can clearly see Sara and her friend eating out of Rice to Riches' iconic plastic bowls with plastic shoehorns.
On their first date before the security guard calls Hitch by his nickname, Sara only knew him as Alex Hitchens. She wouldn't have known his nickname while they were on the jet skis before reaching Ellis Island.
When Hitch first meets Geoff at the zoo, Hitch asks Geoff how he heard about him. Geoff clumsily says Albert Brennaman. Although Sara Melas already made the connection between Hitch and Albert earlier in the film, she or Geoff have no idea that the "Date Doctor" is Hitch at this point and therefore there should have been no way that Geoff knew that Albert knew the "Date Doctor".
In the opening narration Hitch says that communication is 60% body language and 30% is your tone meaning 90% of what you're saying "aint coming out of your mouth" However tone refers to the tone of your voice which does in fact come out of your mouth.