Ravens were the underdogs +3.5.. meaning they could lose by 3 or less if you took them and still win.
niners were giving 3.5 so they had to win by atleast 4 if you bet them
looking back it seems like a no brainer but the 9ers were considered the superior team talent wise plus the ravens had played more snaps than any team in playoff history (i think) so it was assumed they would be worn down while the 9ers had the benefit of the bye... thats why the bookies made the 9ers favorites... it was 4 early in the week and went down to 3.5 so money did pour onto the ravens side to move the line