When Dr Who goes wrong

The problem with Doctor Who is that, no matter how good it is, there's always something that spoils a perfect story.

Sometimes it's a teeny thing - for instance, in the gripping The Loch Ness Monster the only problem is sadly, the Loch Ness Monster. Sometimes it's a large thing - like letting Richard Martin direct.
 
For the Not-We, it's hard to explain Richard Martin. However - if you think that Dr Who is always rubbish, believe me when I assure you that Richard Martin produces a special sort of rubbish. He's the Ed Wood of Dr Who - always trying to depict an apocalyptic action adventure when he has trouble just keeping the heads of his cast in shot. People get shot and forget to die, he has trouble keeping a dalek in focus, and came up with the genius of depicting an alien planet by smearing vaseline over the lens - resulting in six weeks of squint-induced migraines.
 
Anyway, the reason I'm going off on a fanboy rant is that sometimes Dr Who gets spoiled by the tiniest of things. The Silurians is a gripping thriller about an alien civilisation - it's full of great characters, strong sets, intelligent plotting, low-key effects, good camerawork, and nice monster suits.
 
And what ruins it?
 
Why, one simply thing.
 
Someone at some point told the people playing the monsters: "It would look really great if you twitched like palsied pensioners."