Bone to pick

As everyone has experienced, bones, especially fish bones, can be problematical. Therefore, bones have been synonymous with problems or difficulties and have been used in this figurative sense since at least the 15th century. Having a bone to pick, or to pick a bone with someone, dates from the mid-16th century and refers to a problem or issue that needs to be discussed and resolved. See also Bone of contention, Make no bones about it, and Pick the bones out of that.