I would have to say about five minutes ago, outside my house. We live in the middle of nowhere next to the highway. The highway was dead. Hell, EVERYTHING was dead. The fog was so heavy that I could barely see more than 10 yards (I'm not exaggerating). There were street lights piercing through the trees, and this big fluorescent one by our house wasn't doing anything but turning the fog into this impenetrable white sheet. And the frogs... They didn't even croak like normal frogs. We always have them down by our pond at night, but this was different. They were all simultaneously alternating between two low, eerie notes. In some cases, a flickering street light is extremely creepy, but that would have actually made this even less so. Everything was just so perfectly still, and it all contributed to this deadly motionless atmosphere. It didn't feel like you were going to attacked by some monster. It felt more likely that you would fall over dead, still, and join the rest of the setting.