Part 2 of 2.
So, last week we left The Doctor and Donna watching as Earth was slowly being gassed by the Sontarans, and Martha had been replaced by a clone.
1. Apparently The Doctor is so busy thinking of saving the world with his sonic screwdriver, that he doesn't think to free Wilfred from the car with a blow to the windscreen. Note that later Doctor keeps a mallet and hammer in the TARDIS.
2. Notice Rose's face appearing on the screen as Doctor established communication with the Sontaran ship (and also with Donna in the TARDIS) - mouthing the word "Doctor".
3. Amazing how Doctor seemed to know that the Martha running around was a clone. Also that Sontarans can't clone rings.
4. Perhaps an argument against nuclear weapons - when humans have their grubby little paws on them, they want to play with these toys! 
A fantastic episode, showing The Doctor that sometimes it takes more than a sonic screwdriver to save the world!