Android framerate increases a little when I put my finger on the screen. What?

While trying to optimize my simple 2D game on android, I'm noticing a very strange effect.

If I just let it sit there, the framerate hovers around 30-40FPS

If I place my finger on the screen the framerate hovers around 50-60FPS

I have already disabled all UI elements and scripts that care about touch.

What could be causing this effect?