When injecting in appropriate areas, you have the possibility of poking through some small veins. When this happens, some blood will push out of the injection site, sometimes it may squirt with trajectory, nurses hit vessels, veins all the time, that's why they pull the point out with a cotton ball over the injection spot. If you inject INTO a larger vein or vessel, you run the risk of a possible embolism. (It's like a stroke in your brain, or your heart will go into arrest) Read up on injection sites, and don't deviate from the obvious suggested sites. Bro