Answer
The appearance of the harmful isomer must be due either to spontaneous isomerization in the body or to its promotionn by some enzyme present in the body for some other needed function.
Work Step by Step
The important point here is to see that isomerization happens naturally in aqueous solutions, such as those in every cell in every living thing, and so that is the most likely explanation for the appearance of a non-consumed isomer of thalidomide.
