I flew into Chicago from the UK a few months ago. A guy a few spaces behind me in the line had a search dog stop at his feet. He had some fruit in his bag. I can't remember what it was, an apple or something. They gave him a form to fill in and he had to pay a fine.

I had a banana in my bag. A very ripe one. But the bag was on my shoulder rather than on the floor by my feet so the dog just walked straight past me. There's a hack to remember.