Here is an image of the internal working of the nail. Don't start going to short, clip more than just the tip, but don't hack at it. Once you get blood wipe the first little bit off and the squeeze the toe to get a droplet. smire the blood onto the card and then use ether the setic powder they sell for cuts or corstarch or flower works too...I use cornstarch at home. Apply pressure to the nail tip with the powder till the bleeding has stopped. The nail will be sore for a few hours or so, and don't let him sit on ruff surfaces or chew at the nail, this could cause it to start bleeding again.
I just did the DNA test on my Elmo the other day and he was fine, he didn't look like he was bothered by it after about 20 minutes.