Approximately 54 minutes into the film, Rick goes to see Farari at "The Blue Parrot." A bottle is delivered to the table and Farari pours a drink, carefully replacing the cork. In the next shot, the cork has magically disappeared!
This movie is apparently stuck on this slip up...In the scene where Rick is having Sam play "As Time Goes By" after seeing Ilsa and she then comes back to Rick's place to see him after they have closed the cafe, he repeatedly refills his glass from a bottle that has the cork in it but never takes the cork out.