Dramatic Coffee Drinking
One of my favorite parts of this movie is when General Mann is in the bunker and talking with Dr. Forester. He's telling him how once the martians go into an area, no further information comes out. He pauses and dramatically lifts his coffee cup up to his mouth. He's also holding cup in a weird way as to make it even 'more' dramatic.
I love it because it's an absolutely perfect point to add some great slurping sound effects. It's nearly as good as a bunch of martians using a giant screwdriver and running in a circle to unscrew the cylinder hatch from the inside.