When an odor has been in or on an item and then been removed; it leaves an odor behind, like a spilled beer on a backpack.
Example: Our canine has an alert in a junior high school classroom on a backpack. The young girl comes in and admits that is her backpack. After some conversation, she explains that beer was spilled on the backpack by her stepbrother the night before. The principal sends the girl to the counselor to talk about what was going on. The young junior high girl confesses to the counselor that her stepbrother is sexually molesting her night after night while he is drinking. She doesn’t know how to make it stop. Now that the school knows; they got her help!