I did a search for a word in the Toxicity field but got no hits, even though I know the word exists in the field.
Although the viewing form displays text in this field, the Toxicity field in the search interface is a number field. It only searches for numbers. If you want to search for words that appear in this field, you must search for the words in the "Properties (full text)" field. No * is necessary, it does stemming automatically, so for example, a search for rat will get you rat or rats.