Yeah this is something I've been tracking for a while now. My cat Milo goes absolutely rigid about 30-40 seconds before anything happens, ears flat, staring at a fixed point in the room. Not at the object that moves either - somewhere else entirely, which I find really interesting.
Makes me wonder if they're picking up on something we can't detect, like infrasound or some kind of electromagnetic change in the environment right before an event kicks off. There's actually a fair bit of research suggesting animals detect these things before humans do, earthquakes being the obvious example.
Has anyone been keeping any kind of log of the timing between animal behaviour and the actual event? I started noting it down but my sample size is small. Also curious whether its always the same animal in your household that reacts or if multiple pets pick up on it simultaneously. Would love to compare notes with people who've been observing this longer than I have.