Snakes don't feel injections like you and I would. I actually had to give my 5'5'' boa injections for an RI and had absolutely no problems with it. She acted like she didn't even feel it---which I don't really think she did. Just make sure to get the needle in between the scales and into a muscle. You can usually find a muscle running on either side of the spine. The hard part is just keeping them still long enough to stick them.