yes this does happen, its mainly from penetrating through a vein. IF you would not of aspirated and simply injected, the oil would of blown out or blown back the vein and the gear would of still ended up in the muscle end not in the blood stream (though you would of had a bruise). of course a little bit of the Tren may get into the blood stream ,, thats when your lungs begin to burn your body gets all flushed and you can't breath for a good 15 mins. fun stuff