While a cat eating a small amount of mustard is highly irritating, it usually won't cause immediate death. However, the irritation from the mustard may cause a range of adverse reactions in the cat, such as tearing, sneezing, vomiting, and drooling.
In addition, mustard may cause a burning sensation in a cat's esophagus and gastrointestinal tract, leading to hoarseness and affecting the balance of gut flora, which in turn can cause symptoms such as indigestion, loss of appetite, and diarrhea.
