I use a butter knife. Thin, and dull edged. One side of the tab is a square bottom "U", and the other side is a wedge w/ a flat lip.
You have to apply downward pressure, and twist the blade between the 1/2's.
Start in the center first. That way IF a tab breaks it will not show up later. Once you see which 1/2 has the "U" shape they will pop apart easily.