Crying over chopped onions could be a thing of the past. Slicing with sharper blades and slower cuts can eliminate those painful tears, a new study finds. A chemical formed from onion juice (propanethial S-oxide) triggers those tears. Slicing the onion ruptures its cells, triggering a chemical reaction that forms this compound. Chopping can fling tiny droplets of it into the air. If they bind to sensory nerves in a cook’s eyes, they’ll cause that well-known stinging — and tears.  But slicing onions slowly with a sharpened knife cuts the number of tear-inducing droplets that were spewed. This technique could offer serious relief to everyday cooks. It also could shed light on how pathogens spread. The researchers shared their findings on Oct. 21 in Proceedings of the National Academy of Sciences. “This is something everybody’s dealing with,” says physicist Navid Hooshanginejad. He now works at SharkNinja, a product-design company in Needham, Mass. “Now we can also explain and understand it better fundamentally.” High-speed cameras captured droplets flying from onions as they were sliced, allowing researchers …