Here is another very helpful article

http://www.eroids.com/forum/general/general-talk/getting-to-know-pip

There's a bunch pip threads here. Mrs Nitti gave you one. You can use the search tool up top, kinda looks like a magnifying glass, search pip.

What it boils down to is (in order of suckiness, from not so bad to worst) either your muscle not liking the specific carrier in the oil, the hormone crystalizing in your muscle - which is based on the raw being used, the oil seeping out from the muscle or not even hitting the muscle causing sub q irritation, and then finally an infection. Follow sanitary guidelines and you should never get an infection. If you constantly get peg legged, find a different lab.