When Leslie enters the room and sits down she places her drink on the table. When the camera cuts back to her the drink is in her right hand. When the camera cuts again the drink is back on the left side again. After another cut it is back in her right hand and again on the table after another cut.
Before Donna screams, Tom is holding his cup with both hands; after Donna screams, he jumps up, and the cup is nowhere to be seen.