|This article is about an older version of DF.|
When a single dwarf is being attacked by more than one enemy, it may fall into a Martial Trance and supposedly focus better. They will also actively seek fights with enemies and neutral creatures. The symbol for a dwarf in a trance is
! which will flash over his icon.
Toady has stated here  that trances 'obscenely' improve most combat modifiers except direct damage, making the dwarf's effective combat skills for all rolls count as effective skill = (skill+1)*5. They also make the dwarf unaffected by unhappiness and has no need to eat, sleep, or drink for as long as the trance lasts, though this should hardly ever matter. Finally, they allow even blind dwarves to see perfectly for the duration.
Only creatures with the [TRANCES] flag set in their data file will enter trances. Only dwarves have this flag as default.