Anilori said:
Traditional dwarfs can't tell each other's gender, but if I remember well, the clues Vimes picks up are related to the lady dwarfs timidly adopting markers of human feminity (eyelashes etc.), as the Mad Collector said?
Yes, this makes sense. A dwarf who truly wanted to hide her gender wouldn't be able to be 'detected' by Vimes. But those who were using very subtle signs--like Cheery probably did in Feet of Clay, would be 'detectable' by Vimes because he knew, through Cheery and some of the other female dwarfs in the Watch (we know there are some, because they all go ga-ga over Young Sam when he's brought to the station), what to look for.
Dwarfs, on the other hand, because they generally don't care about gender, don't go out of their way to try to distinguish between males and females, and, therefore wouldn't be looking for the "subtle" feminizing signs that Vimes can detect.
[SPOILER AHEAD]
Don't think this is consistent? Well think of Jackrom in Monstrous Regiment. The sargeant knows right from the beginning that all of the recruits are females, because the sarge has this ability. Yet, none of the recruits knows the others are female under they start admitting it to each other or they catch them in obvious acts. An 'outsider' can often 'detect' tells that those in a group can't.
If you don't agree with this, go a poker room some time and watch a table without playing. With enough observation and hands, you'll be able to tell, through their various facial tics, posture, and gestures, when certain players are holding strong or weak hands. This is something that is extremely difficult for someone actually playing the game to do and those who can do it, as long as they have sound skills, generally end up winning more often.
J-I-B