A scientist reckons he's cracked why Daleks are scary - it's because we're worried we might become like them!
Dr Robin Bunce says we're frightened of the Doctor Who monsters because they used to be good, but became bad and lost their emotions.
He said: "The reason the Daleks are evil is because we recognise that they were once better. They are the nightmare future we dread."
Daleks first appeared in Doctor Who back in 1963.
When they were introduced, we were told they had retreated into their metal shells after a terrible war and slowly became like machines, with no emotions.
Dr Bunce from Cambridge University added: "We recognise the Daleks as evil because they have lost all that we hold most dear."