Correction: An earlier version of this post incorrectly referred to rats' toes as rat's toes, implying that burgers only contained the foot bones and flesh of a specific rat.
Although a possibility for a number of beef patties - which would likely have been processed at one facility - it was not the writer's intention to suggest that a small percentage of the meat content in a burger - in the general sense of burger - comprises toes from "some rat", but rather, more than one.
Indeed, the singular "hamburger" denotes not a specific "hamburger" but in this case is presumed to include the plural.
It is what could be regarded as a burger in its most general, Platonic essence.
To further clarify, the word "some" does not refer in any pejorative or dismissive sense to a specific rat (as it is used in this example sentence:
"I read about the scandal in some tabloid rag");
The word "some" - in this context - specifically refers to an undetermined number of toes.
For "some", therefore, you may instead read "a sprinkling of" in order to better appreciate the writer's aim.
The ratio of toe-contribution levels to burger content - although miniscule - would come from vast numbers of nests of rats, spread out over the course of many decades, at hundreds, if not thousands, of meat processing facilities, in billions of burgers.
In summation, then, the new name for Nutella should be Rats' Toes.