"I'll bite" is an expression in English which comes from fishing. What it means is "you have lured me in" or "I'm interested in what you are suggesting" It is usually used when somebody is playfully withholding information. and example: "Hey you'll never guess what I just heard!" "I don't have time for stories right now." "It's about Lucy." "Alright, I'll bite. Tell me." or "Alright I'll bite, why are you acting so down today?" Hope this helped :)

This expression is used when someone has asked you a question that you know will have an unexpected, generally funny, answer that you can't think of. You say it, and the other person finishes the joke or gives the answer.