Oops, too late, have I said too much?..............
There is a technique interviewers may use known as a silent gap.
Basically, they ask a question which could be a closed question (can be answered simply yes or no). However after you give your yes or no answer, they leave a long silence or pause.
This usually makes you feel uncomfortable enough to try and expand on your answer and be too honest.
Be concious if this is happening and if there is a silence, leave a short silence yourself then say sorry, did you want me to expand on that?
There is also something called the horns and halo effects.
The Horns effect quite simply is where an interviewer takes a less favour to you due to one of your hobbies,etc. So unless you are asked, try not to mention to the interviewer that you are a Leeds/ Man U/ Sheffield Wednesday supporter or anything else that would cause a conflict or debate accross a pub table.
The Halo effect is the opposite, ie when you have written on your CV you enjoy motocross in your spare time, and the interviewer is into the same thing.