the Metro stairs, sprint to the Farecard machine, feed it a $5 bill and wait for it to spit out my boarding pass. Instead, it spits out my $5 bill. Rejected again.

Well, I'm used to this. My Metro experience has taught me that all dollars are not created equal. Crass humans may care only about the denomination of their currency, but these machines are mechanical esthetes; they won't deign to accept a soiled or wrinkled bill. I check out the five, searching for flaws. Finding none, I smooth it out and feed it back into the machine.

Out it comes. I hear my train rumbling into the station. Mumbling Luddite expletives, I examine the bill more closely and still find no marks, no rips, no wrinkles. This is a wonderful $5 bill, a perfect $5 bill, the kind of $5 bill you can bring home to meet Mom. Again, I slide the bill into the slot. Again, it comes right back out. I hear my train rumbling out of the station.

Cursing more audibly now, I move to the next machine. This one seems more democratic. The guy in front of me feeds it two $1 bills that look as if they spent a long night on a wet bar. The machine eats them up and spews out a Farecard. Beautiful. I feed it my fin. No go. Out it comes.

Time to check my wallet. Two twenties and a ten. I'm loaded, but these petty robots can't handle serious money. I walk to the booth seeking change. But the man in the booth doesn't dispense change, he dispenses advice. "Rub it on your shirt," he says. "That sometimes does the trick."

Well, okay. I rub the fiver on my shirt, then slide it into the machine. Out it comes. I rub again, insert again. Out it comes again. I hear my train rumble into the station. I rub the bill some more. By now, I've rubbed so hard that Lincoln is clean-shaven. But still no luck.

I put down my satchel so I can use both hands for this rubdown. I rub the bill on my chest, knead it, massage it. Suddenly a thought pops into my head: I'm a grown man and I'm standing in a Metro station at rush hour, making love to a $5 bill. What would Krafft- Ebing say about this?

Now dangerously close to committing an act of machinicide, I slip the bill into the slot again. Bingo! Out comes a Farecard. The blasted thing has been teasing me all along. I grab the card and sprint for the platform.

As I run, I could swear I hear a mechanical titter, the sound machines would make if they could giggle. But of course they can't, can they?

Besides, that sound is quickly drowned out by the racket of my train rumbling out of the station without me.