The public institutions are eating the marshmallow and the marshmallow is the public funding available to them, whether it's from taxes, foreign aid or bribes extracted from ordinary people. Eating it is taking the public funding for their own personal use, or offering tenders to friends who have no intention of actually doing the job.

Here's the first result that comes up when I do a web search for "how corruption works", it's pretty informative for those who are unfamiliar with the concept: https://www.transparency.org/en/what-is-corruption