Checking a gender discrepancy, scanning the person, and discovering that there isn't a gender discrepancy.
Some of the crazy aliases / fake names that travelers come up with.
Sometimes you can get a traveler who is flat out obvious with his discrepancies, and who actually is pretty humorous even when you deny him entry. One of Jorji Costava's attempts to get past the check point is to give you a passport drawn in crayon.
The best part comes when you let the fake passport go through.
One United Federation foreigner will tell you he used to be an inspector like you, saying that the UF border control is now computerized. If he doesn't have all the documents in order though (necessitating denial), he'll nonchalantly agree before quipping, "So this is what it feels like", and then walk off.
"It is all done by computers now. They can deny much faster that way."