When using this technique, you can also get some images of the cheliceral teeth, which are sometimes necessary for identification. You need to sort of make the spider mad, though, and push your shish kabob up against the base of the chelicerae (not too hard!). This will prompt it to become a little defensive and it will flash its fangs and spread its chelicerae, leaving the teeth visible... just have your camera ready in your opposite hand. If you have a "helper" that always helps, so they can take the image for you. But I'm a little stubborn in that sense and prefer to take my own photos, no matter how awkward it is with one hand.

If you do this all correct and with just the right amount of gentleness, the spider will be free of any harm. You can slowly release the pressure on the cotton ball. The spider is too stunned at this point and isn't going to "jump" out or anything. They usually barely even move at first because (maybe?) they're testing their boundaries. It will start to move a little more, and then that's when you release it back into the jar or whatever you're keeping it in. The reason for doing it slowly is because their legs can sometimes get twisted and any sudden jerk will prompt the spider to drop its leg off (yep, spiders do this, just like lizards can drop their tail off).