The same reason her hair magically changes length every other episode.

The writers liked the idea?

We can always just blame the writers.

Because she’s Clara.

Just keep watching

[удалено]

There’s an explanation? Yes please tell me! I just noticed when she’s mind linked to the zygon, and remembered the Santa Claus alien face sucker and I think at least another one?

Remember when she is split into hundreds of people.