The reason could be that the chaat was contaminated by pathogenic micro organisms. The unhygienic conditions present near the shop becomes
the breeding place for microbes, flies, etc.
The pathogens can be transmitted to places by flies and other vectors, even the utensil used for serving could have been contaminated by the
pathogenic micro organism. If such microbial contaminated food is consumed several disease like diarrhoea, dysentery, cholera, etc., may occur.