Going from FLIES = 1 -
OVINE = 0,________FLIES____________Not ??I??
GAMES = 0,_______FLIES____________Not ??IES
The one point (in FLIES) must have come from either the F or the L
VALES = 0_________________________Not ??L??
FILES
If 0, then ?L??? as the only thing that could have contributed to the point in FLIES that changed was the L.
If 1, then F???? as changing the L around, the only other letter that could have contributed to the point in FLIES, did nothing
Edit - Made easier to read