When Guybrush meets the guy sunbathing at the Brimstone Beach Club - and tricks him into thinking he's sun-burnt - Guybrush says 'Palido, you're burning!' However, even if you have not previously found out Palido's identity from Slappy Cromwell or from engaging Palido in conversation, Guybrush will still call him by name.
When Guybrush places the uncursed diamond ring on Elaine's finger she punches him. When they hug each other a few seconds later, the diamond ring has vanished from her finger.
On the billboard outside of the Goodsoup Hotel, it says "Griswald". This is incorrect since Griswold is spelled with an O instead of an A.
Hard cheese does not contain lactose.
When the Flying Welshman asks Guybrush where Scabb Island is, he says "East by North-east". But according to the official map of the Tri-Island Area on The Curse of Monkey Island manual and the Lucasarts logo in the opening credits scene, Scabb Island is West by North-West.
The previous game Monkey Island 2: LeChuck's Revenge (1991) ended very strangely: Guybrush finds himself as small kid with his "brother" LeChuck and his "parents" in an amusement park. In the beginning of this game, Guybrush is on the sea in a floating bumper car. No explanation is given what happened in between.
When you talk to Griswold about being a Goodsoup, he will ask you for your name. Once you select a fake name and then die, you are put to rest in the Goodsoup Family Crypt. However, when you show Stan the death certificate with your fake name, he doesn't object even though he knows your name is Guybrush Threepwood.
In the Goodsoup Hotel, when you make Madame Xima place down all the cards, Guybrush picks up one telling her that there is a three-headed monkey behind her, so she turns her head. But when he picks up the remaining cards, he simply picks them up without even saying anything, however she still turns her head.
Guybrush pays Griswold for the first drink at The Goodsoup Hotel. However, he doesn't pay for the next.
When you create the compass and give it to The Flying Welshman before you start talking to him, he gives his identity and tells Guybrush that he is The Flying Welshman. If you hover your mouse over him, he is shown as "mysterious figure". And when you start talking to him, Guybrush asks who he is, even though he already knows his name.
There is an error when Guybrush is El Pollo Diablo. If you try to go to the Brimstone Beach Club using the normal route, depending on whether you kicked the Cabana Boy out, he will immediately notice and send you way. However, if you enter through the gate next to Palido then go around using the shortcut, you can show up at the club and the Cabana Boy doesn't react to you. In fact, you can even talk to him and have a normal conversation (even though dialogue options are omitted since Guybrush already completed everything he needed to do with the Cabana Boy.)