"Only the blood you shall not eat": There is (transgression of only) one negative commandment (in eating the blood of disqualified offerings) and not two.
Since in offerings blood is compared to fats — viz.: Just as in (eating their) fats there is transgression of two negative commandments, so in (eating their blood) there is transgression of two negative commandments — I would think that the same applied to (eating the blood of) disqualified offerings; it is, therefore, written "Only the blood you shall not eat" — there is transgression in it of only one negative commandment and not of two.