Smack that is an intramuscular injection with moderate action time. Is to inject the drug into the muscle and let the small blood vessels in the muscle slowly absorb it. The common parts of intramuscular injection are the arms and buttocks, and the gluteal muscles are often chosen, because the gluteal muscles are thick and difficult to puncture deep blood vessels. There are many nerves around the buttocks to avoid hurting them. The needles on the buttocks are all on the outside of the unilateral buttocks.