A biopsy is done to determine whether Leo has Hirschsprung’s disease.
The nightmarish image won’t go away:
" . . . after removing the part of the colon that lacks neurons, the rest of the colon is pulled through to the outside of the stomach and sewn to the skin with the mucous membrane exposed. This creates an „abdominal anus”, or a stoma. Excrement passes through the stoma into special bags glued to the skin around the stoma."
Source: Polish Wikipedia
Hieronymus Bosch "The Garden of Earthly Delights" [fragment]