During the x files title opener in each episode as theme music plays sequence when it says paranormal activity what is that thing animating on both sides of picture?

You're likely thinking of the two sets of swirling black and white patterns that animate on either side of the screen during the "Paranormal Activity" title card in the *The X-Files* opening sequence.

These patterns are actually fractal visualizations, created by a computer program. The exact nature of the fractal patterns changes from episode to episode, but they're always abstract, swirling, and ever-changing, contributing to the show's eerie and mysterious tone.

They are not actually a specific "thing" but rather a visual representation of complex mathematical patterns that evoke a sense of the unknown and the vastness of the paranormal.