At work one day, my coworker, my boss, and I witnessed a cup suddenly slide off a completely flat table, as if pushed. Nobody was anywhere near the cup, and we checked the surface thoroughly for moisture or anything else that could have caused that movement. We couldn’t come up with any explanation for it at all.
My older sister had a similar experience, also with coworker witnesses.
I consider myself somewhat of a skeptic, but I’m glad I got to experience something unexplainable firsthand and with other observers. Reminds me that there’s still plenty of stuff we goofy hairless apes don’t have all figured out.
The only vent is across the room from where the cup moved. However, the bottom of that cup is a raised base that is basically its own downturned cup. I suppose a pressure differential may have formed!