The aliens' beam weapons had some pretty strange interactions with matter. Organic life gets reduced to dust, but the clothes on humans are left untouched, and yet the beams punch through other solid matter with tremendous effect.
They use two different kinds of beam.
What exactly is the significance of the birds throughout the movie (flying towards the Tripods during the ferry scene and again towards the end, shown at one point eating the Red Weed, etc.)? Do they actually play some role in the aliens' downfall, or do they simply constitute Rule of Symbolism?
The birds are what carry the diseases which wipe out the aliens.
What purpose does the Red Weed serve? Food source, or some alien redecoration technique?
Xenoforming. Changing the natural environment fom suitable for humans to suitable for aliens.