throw something in

Từ điển Oxford Advanced Learner 8th

ˌthrow sthˈin derived
1. to include sth with what you are selling or offering, without increasing the price
•You can have the piano for $200, and I'll throw in the stool as well.
2. to add a remark to a conversation
•Jack threw in the odd encouraging comment.
Main entry: ↑throw_derived