American Karl Marx (cw: meat):

According to our assumption the burger has double the value of fries. This, however, is only a quantitative difference, which is not yet of immediate interest to us. We recall, therefore, that if the value of a burger is twice as great as that of 10 fries, then 20 fries have the same amount of value as a burger. As values, a burger and fries are things of equal substance, objective expressions of similar labour. But cooking and serving are qualitatively different kinds of labour. Conditions of society, however, are found, wherein the very same person alternately cooks and serves; and both these modes of labouring are therefore merely modifications of the labour of one and the same individual, and are not yet specific definite functions of different individuals: just as the burger which our cook makes today, and the chicken sandwich which he is to make tomorrow only presuppose variations of the same individual labour. Appearance itself teaches, moreover, that in our capitalistic society a given portion of human labour is adduced alternately in the form of cooking or in the form of serving on each occasion in accordance with the shifting direction of the demand for labour. This changing of form which labour endures may occur not without friction – but it must occur. If one disregards the determinacy of productive activity and therefore disregards the useful character of labour, it remains true about it that it is an expenditure of human labour power. The labour of a cook and serving, although they are qualitatively different productive activities, are both productive expenditure of human brain, muscle, nerve, hand, etc., and are both in this sense human labour. They are merely two different forms of expending human labour power.