I had a small example of the same thing yesterday. I haven't eaten bananas for a long time but over the past few days I had been eating bananas.....I am not being patronising when I say it because it could well be something paristic (which was my first thought too as I thought digestion would have meant no discernable trace of banana) but thinking about it I have eaten bananas these past few days and it looks like the seeds you get in bananas.