When bidding at the auction David offers "1 million dollars" for the hippopotamus. This is not possible since his lawyer stated earlier the fee he would receive for the proposal, which would have been deducted from the million David received for the proposal. Therefore David didn't have 1 million dollars to bid.
When Gage sits at the gambling table with Diana, his chips are in front of him at #12. He slides the chips over to Diana who is sitting in front of #11. When the camera pans back, the chips are still at #12 in front of Gage.
The helicopter that Gage and Diana take off in is supposed to be at the Las Vegas Hilton, But you can clearly see the Lady Luck Casino next door to where it leaves from. The Lady Luck is downtown Las Vegas no where near the Hilton.