When I was a child, I played on my head because the blood vessels in my head were clearly visible (relative to my hands) and it could prevent children from slipping out of the needle, but I also played on my ankles.

Adults usually inject a little intravenously into their hands because they have self-control and their blood vessels are clearer when they grow up, but for some people who are often hospitalized or obese, doctors do not rule out choosing some special places to play.