We have a 9 weeks old puppy, and she's found nothing better to do than to chew on some pebble stones that she finds in our backyard. Is it dangerous for her to chew on them? She takes them around and then plays with them, on some occasions she took then in the house, which we forbid her to do. They are the size of a golf ball usually, big enough to get them completely in her mouth. Could she swallow them accidentally?