Has so much time passed that we can considered Paranormal Activity something that gets thrown back to? (Don’t answer that. I may crumble into dust.) A24’s new horror film Undertone very much plays like a variant on that 2010s-era horror series. While those movies depended on grainy, realistic-looking video footage that could be studied for flickers of malevolent spirits, Undertone arguably goes even more minimal: In this audio-based horror, two podcasters start listening to a series of mysterious audio files.