Use this skill to tell when someone is bluffing or lying to you. This skill represents sensitivity to the body language, speech habits and mannerisms of others.
A successful check allows you to avoid being bluffed (see Bluff). You can also use the skill to tell when someone is behaving oddly or to assess someone’s trustworthiness.
In addition, you can use this skill to make an assessment of a social situation. With a successful check (DC 20), you can get the feeling from another’s behavior that something is wrong, such as when you are talking to an imposter. Also, you can get eh intuition that someone is trustworthy and honorable.
No, though you may make a Sense Motive check for each bluff made on you.
You can use Sense Motive to detect that a hidden message is being transmitted via the Bluff skill (DC equal to the bluff check result of the sender). If your check beats the DC by 5 or more, you understand the secret message as well. If your check fails by 5 or more, you misinterpret the message in some fashion.
A Sense Motive check may be made as a reaction to another’s Bluff check. (When that is the case, your DM may roll your Sense Motive in secret, so you don’t necessarily know someone is trying to bluff you. Using Sense Motive to get a sense of someone’s trustworthiness takes at least 1 minute.