In the scene when Tom Hanks and Danby Colby are on the boat discussing the women in their life, Tom Hanks fixes a drink. The camera goes to Danby then back to Tom mixing the same drink again.
This really isn't a mistake. I think he is still mixing the same drink so that it gets all the way mixed. If this was a slipup, I think they would have noticed it and taken it out.
So maybe Tom wants to mix the drink properly--I can understand that. But why does he put an olive (or onion, I forget) in the drink, and take it out, and put it back in again. Look closely, the first drink already has an item of food in it, it's the same glass that he puts something in two times.
Yes, it's a real slip-up. He mixes the drinks fine - the slip up is after they are poured. He puts an onion in his dad's glass and an olive in his. After a cut-away, he is again putting an olive in his olive-less glass. Chapter 27 on DVD.