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Butterfly sets contain air within the tubing. If the anaerobic bottle is inoculated first, this air can enter the bottle and compromise anaerobic conditions, reducing recovery of obligate anaerobes. Therefore, with butterflies, inoculate the AEROBIC bottle first to vent the air, followed by the anaerobic bottle. Option B is correct. When using a straight needle (no tubing), many institutions inoculate anaerobic first—confirm local policy—but the key butterfly nuance is to purge air into the aerobic bottle. Always disinfect bottle stoppers with alcohol after skin antisepsis, collect recommended blood volumes (a major determinant of yield), and obtain multiple sets from separate venipuncture sites when ordered. Draw blood cultures before other tubes (cultures first in the overall order of draw) to avoid additive carryover. Accurate site/time labeling and prompt transport further reduce contamination—high-yield details on certification exams.