The vegetable known for making you cry when cut is the onion. When onions are sliced, they release a compound called syn-propanethial-S-oxide, which vaporizes and irritatingly hits the eyes. This irritation triggers the lacrimal glands, leading to tears as a protective response. Onions have a unique chemical composition that varies depending on the type, with some, like sweet onions, being milder and less likely to cause tears compared to stronger varieties. There are various techniques to minimize tearing while cutting onions, such as chilling them beforehand, using a sharp knife, or cutting them under running water, although personal experiences may vary.