Flag to Ensure In Vein and No Blockage

Flag as usual to ensure that needle is properly inside a vein.
Blood entering syringe shows that you are in vein, and that the needle tip is clear of blockage.
You can now begin injecting.
Keep a slow but steady pressure upon plunger as you inject. You want the liquid to keep flowing.
Do not re-boot. Just inject it all in one smooth go.

If you are missing you will instantly see because surrounding tissue will immediately react and ballon.