Fly/go off at a tangent phrase
A tangent is a straight line that touches the outside of a curve but does not cross it.
To suddenly move away from the main topic you are addressing or discussing and to think or talk about something else.
When the lecturer was talking about maths, he went off at a tangent and narrated his adventures in Africa.
So far, he has gone off at a tangent two times in this speech. If he does it one more time, I will quit.
The verb "go/fly" must be conjugated according to its tense.
This phrase dates from the second half of 1700s.
If you swallow the bait, you take something that someone offers you, or agree to do something that someone asks you to do without knowing that it is a trick or way of getting something from you.
You can't just do whatever he wants you to do. Don't swallow the bait.