The term 'LAB WARNING' can be broken down into three crossword solutions: BARK (4 letters), ARF (3 letters), and GRR (3 letters). These words are all onomatopoeias, which are words that imitate or suggest the source of the sound that they describe. BARK is a sound made by a dog, ARF is a sound made by a fox, and GRR is a sound made by a bear. All three of these animals are commonly used as warnings in laboratories, hence the term 'LAB WARNING'.