Before. To heighten their triumph, the Philistines waited until the last moment before they revealed the secret that they had forced from him through his wife. Their answer, like the riddle, is in poetic form.
Plowed. Samson quickly perceived his wife’s treachery, and showed that he did so by quoting the poetic proverb of plowing with another person’s heifer. They had not used their own wit to find the answer to his riddle, but had learned the secret from one close to and belonging to him. The statement is an assertion that if they had acted fairly he would have won the wager.