In various scenes where the maggots are moving, such as when the Doctor is using his sonic screwdriver to rescue Jo, you can see the false ground with straight grooves where the maggots were operated by stage hands.
When Benton rescues Jo and Cliff from the enclosure, the ground outside moves slightly revealing it to be false (the ground was made with tracks in it so as to enable the giant maggots to move, then covered with soil).
The Doctor tries to save Cliff by giving him a broad-spectrum antibiotic. However, he previously established that the Green Death kills people as it is a virus. Antibiotics don't work on viruses, only bacterial infections.