Generally, biceps exercises are set up so the upper arms remain roughly parallel to the torso and the resistance reduces as the hands get closer to the chest. Think of the standard barbell curl.
But the guillotine curl requires the upper arms to be positioned perpendicular to the torso with the shoulders flexed – arms forward with respect to the torso.

This position makes the resistance grow stronger – instead of lessening – as the cable moves downwards toward the body. Hold and squeeze the biceps at the peak contraction for two seconds.
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Try this rotational exercise to build real-world core strength. Bonus: Thick obliques are sexy.
Since I've started writing for the T-Nation, I've gotten 100's of e-mails asking me varying questions about the rotator cuff and its many somewhat magical qualities. While it may not be as cool as big quads or a great set of guns, a well-developed rotator cuff is sexy in its own, injury-free kind of way.
Now you want her to join you in the gym because the couple that trains together, stays together.