A: This may happen if the injection is a little shallow and does not penetrate enough of the cat's skin and some of the GS is collected under the skin. To avoid this situation, be sure to inject in the subcutaneous region that is below the skin. We have a video on YouTube that demonstrate how to properly perform an injection ( https://youtu.be/vR39MSFsrnE ). The lump will disappear slowly, usually within a few hours or a day. If there is any GS leaking from the skin, the area needs to be cleaned with alcohol swabs or wipes.