Dreamed I was at a Nebula Awards banquet and (there is no explaining dreams) one of the officers. However, there was a glut of SFWA officers present, all getting in each other's way, so I quietly slipped outside. On a balcony off the hallway, I saw Michael Dirda looking down two great black 19th-century steam locomotives in the rail yard below. We were both eagerly looking forward to taking part in the train duels later that night.
"The rail guns those things carry will launch a projectile at 1,200 meters per second," Dirda said in a tone suggesting he never ceased to marvel at human folly, "yet if you walked down the aisle with an ice cream cone, they'd fine you for it."
On awakening, I checked the numbers and found the projectiles would be traveling at almost four times the speed of sound. But I've never had any mathematical ability whatsoever when asleep.