Costa Coffee Recalling a Number of Sandwiches + Wraps Possibly Containing Stones

Now we have another food product recall , this time it is at costa coffee

Four of its lunch products could possibly contain small stones !!

These are Costa Chicken & Bacon Caesar Wrap, Costa Southern Fried Chicken Wrap, Costa Chicken Salad Sandwich and the Costa BLT sandwich

The question is in what part of the packing process can small stones come from ?

I understand metal pieces or even glass, which might come from machinery breakdown, but stones

Do they make the sandwiches on a pebbled beach somewhere ?

www.chroniclelive.co.uk/whats-on/food-drink-news/costa-coffee-food-recall-sandwiches-27683020