Roots: The Presence of the Past and Rupert Sheldrake's theory of morphic resonance (the Doctor's anecdote about the blue tit behaviour of opening milk bottle caps is a popular example used by adherents), The legend of Pandora's Box, Genesis (the Garden of Eden, Flood's monologue "How do things begin - with a word?" recalls Genesis 1:1). The Doctor quotes Sir Walter Scott ("nothing is more the child of art than the garden")
Technobabble: a fission detrax.
Dialogue Disasters: "You're playing God on an unknown planet - time to pay the piper" (what??)
Dialogue Triumphs: "Blue tits!," "What?" "Blue... Tits," "Is this a Gallifreyan term of abuse?"
"The most evil species in the universe were created by a pitiless cripple whose own frustration and bitterness were reflected by his creations. Another race of killers chose to reject their humanity in pursuit of survival, and so it goes invariably - each and every time it comes down to a nexus point, a moment of decision. A split second where the balance between good and evil is tipped the wrong way. I have spent most of my life hunting those moments down."
Goofs: How does Flood know L'da's name after scanning C'rizz's mind, but not that he has been inoculated?
Continuity: Endarra is the uninhabited twin world of the planet Caludaar and is regarded by the Doctor as the closest thing to the Garden of Eden. According to legend, the Caludaari nearly destroyed themselves through war, and in the aftermath, they vowed never to sully Endarra with their presence. Endarra has a native primate species which has developed tool use and the concept of sharing resources; it can mimic some human vocal sounds. Favria. is the fourth world of the planets' system and was home to a human colony - that colony's destruction was imprinted on the planet as trauma. The child Galayana was the last to die on Endarra due to her resistance against the disease, and so the planet's morphogenic field absorbed her, transformng her into an elemental avatar of 'balance' against the evil of the destruction, and an agent of revenge.
Saravin is a substance used in chemical warfare and was outlawed and destroyed in a few centuries' time after Ventriki militants use it on the planet Crestus V. Four billion years ago the human population of Endarra, the remains of a Favrian colony, were wiped out by wanton dispersal of saravin canisters by [the Doctor surmises] a passing ventriki cruiser.
Jelna wasps will not react harshly if only disturbed once, however if disturbed further will sting their foe to death. In the language of the people of Cakudaar 'Yaranaa' means 'the soul of the vengeful.'
Lambda radiation is extremely unstable.
All junior Time Lords are cautioned against visiting newly-formed worlds because of the risk of 'imprinting' - the Doctor says he was sure to take notice of that.
The TARDIS gardens were designed by the Doctor using block-transfer computation but nevertheless need to be tended - it contains bougainvillea, Draconian myrtle hedges and Vendican bladder-pods, plus a stream and set of swings. The Doctor says he once allowed an entire incarnation to pass without maintaining it.
The Doctor attempts a form of telepathy to read Galayana's mind. He carries jelly babies with him and says he is partial to the red ones. He believes his current body heals faster than his previous one.
Untelevised Adventures: The Doctor says he picked up his musical pitch in 'Memphis' (presumably the one in Tennessee)
Links: The Creed of the Kromon (C'rizz recalls killing L'da). The Doctor refers (obliquely) to the creation of the Daleks and the Cybermen in discussing 'evil' races.
Location: The planet Endarra
The Bottom Line: With its talk of experiments and sealed off worlds Scaredy Cat sounds and feels like a refugee from the Divergent Universe arc. Not much has evolved here, but at least the story isn't too long.