A blood trail was a technique developed by the Nightsisters of Dathomir. With this technique, the Nightsister would use her own blood to mark her target (often a slave) and track them through the blood mark using the Force in case they escaped. The shed blood used for a blood trail could not be removed once the trail was set
"Io comando le madri vecchie di darmi la forza, la spirita, la potenza necessaria per vincere la battaglia che sto per affrontare. Jaa le’mita, ozuye le’mita, mae siman ta. Si tratta di una grande potenza che ho bisogno adesso. Antenati mi danno la forza insieme. Ay'eyh ta nimawa, mae'wa. Ay'eyh ta wa, mie’yebo. Concedimi la mia richiesta in questo momento! Jaa’mae...
Translation: I command the old mothers to give me the strength, the boost, the power needed to overcome the struggle I am about to face. Love of mine, warrior of mine, I mark you. I require great power now. Ancestors give me the strength. Where you go, I go, where you are, I will follow. Grant me my request at this moment! I love you..."
Firmus Piett (LadyVader) is one of the only known non-Nightsisters to have used a blood trail to track someone. He set a blood trail on his own son during a hostage situation and used the trail to track him and his captors two galaxies away.