Measure Foe (Combat)Source Ultimate Intrigue pg. 86
You can read a foe’s martial skill from its body language.
Prerequisites: Street Smarts, base attack bonus +1.
Benefit: You can attempt a Sense Motive check as a free action to deduce a foe’s martial training after observing the foe’s movements for at least 1 minute or observing the foe’s attacks for at least 2 rounds. You take a –10 penalty on your check if you are observing movements, rather than attacks. The DC equals 20 + the creature’s base attack bonus or 10 + the creature’s Bluff or Disguise modifier, whichever is higher.
If you succeed, you learn the foe’s base attack bonus and one combat feat it has, and you learn an additional combat feat it has for every 5 points by which you exceed the DC. You also gain a +1 insight bonus on attack rolls against that foe and to your AC against that foe until the foe gains a level or otherwise improves its abilities. If you fail this check against a particular foe, you can’t try again against that foe until you gain more ranks in Sense Motive.