This document discusses the antibacterial properties of onions and advises against consuming leftover onions. It shares a story of a doctor discovering that an onion absorbed bacteria from patients with the flu. Additionally, it warns that onions left out after being cut can become highly toxic due to bacteria growth overnight. Finally, it advises never blaming mayonnaise for food poisoning from picnic potato salads, as onions are more likely to blame due to being a magnet for bacteria.