As a surgeon, Tomas spent every day with human bodies. He cut them open with a scalpel and inspected what was underneath. Of course, Tomas’s job at the country clinic wasn’t exactly medicine in his opinion, so quitting was no big deal. Still, the narrator says, it seems as if Tomas made the decision too quickly and was, perhaps, missing something important.
Kundera frequently uses the analogy of Tomas’s scalpel to represent the idea of finding something hidden or otherwise covered up. Elsewhere, Tomas takes a metaphorical scalpel to his mistresses to find the ways in which they are unique, and just as the regime forces him to give up his literal scalpel, his relationship with Tereza forces him to give up this symbolic scalpel to some extent.