Gemara itself in Bava Kama page 17 and 18 brings a Tosefta

The Gemara itself in Bava Kama page 17 and 18 brings a Tosefta that is clear that if a chicken chews at a string holding a bucket, and the string is severed, and the bucket falls and is broken, that the owner of the chicken pays half damage on the string and bucket because it is unusual for the chicken to be chewing at a string. However, if the string had dough on it, it would be full damage for the string, and the question about the bucket is left in doubt. Rava had a question if you go by the beginning or end, and so if the bucket would be full damage that would show you go by the original first force. [The question was if an animal steps on a vessel, and it is rolled away and is broken on a stone. Is that full damage or half? Do you go by the first cause or second cause? If you go by the first cause that is full damage, but if you go with the second cause, that is half damage. But the first cause in this cause is not unusual. For it would be unusual that would be half damage.] We do not think that Rava would have asked a question that had an obvious answer. Therefore, the Gemara says the case of the Tosephta is that the chicken is pushing the bucket until it falls is broken so that is direct cause of the damage and so pays full damage and we still do not have an answer to Rava., however the Gemara also brings a proof from Raba [not Rava] that we do go by the beginning of the damage, and not the secondary cause, so the bucket would be full damage. The Rambam decided like Raba that we go by the beginning of the damage. The problem that I see here is that the way the Rambam writes this halacha does not seem to correlate with the Gemara. The Rambam writes, “If chickens were chewing on a string, and it was severed, and the bucket was broken, one pays full damage for the bucket, and that is if it rolled because of them until it fell and was broken. And if there was flour or dough on the string, he pays full damage for the string also.” From this it seems that he pays full damage for the bucket even though there was no dough on the string. But that cannot be so as we see in the gemara where that case is brought openly, and it is stated that that is half damage. Only if there was dough on the string, that would be full damage also for the bucket, since it is not unusual for a chicken to chew on a string with dough on it. And the Rambam and Tosphot both say in a case of force of a force that one is not obligated at all as the Gra brings in his note on this Gemara. so, the law is clear that if the chicken chews on the string and its breaks and the bucket falls and is broken, that is not obligated in damages at all. So, you have to read into this halacha the idea that the chicken was pushing the bucket until it was broken. Another possibility is that the Rambam holds like the Rosh that force of force is obligated to pay full damage in our case of the chicken and the bucket. It might be that the case of the dog with the loaf, the Rambam might not be thinking that that is force of his force, but an unusual act, and therefore the law is different. This would mean that the simple way of reading this law in the Rambam might be what the real intention is. But then why would the dog with the loaf with a coal inside be not obligated? There is perhaps a possibility that it unusual act. A person lighting a fire is usual, but a dog is unusual. and a dog with a loaf is one more degree of separation. But then it would be second degree unusual. But why would that make any difference? Pebbles are is obligated not because they are unusual. I think the Rambam in the case of the bucket with the chicken is going like the Rosh [R. Asher] that force of force liable full damage but the case of the loaf is not force of a force but rather the Rambam is saying that r Yochanan and Reish Lakish are arguing about the reason for fire but not about the law of the Mishna. To R. Yochanan if the dog put the loaf with the coal on the tack, it is liable for half damage; and Reish Lakish says if the dog did not put it down but rather carried it along the stack the liable only for the trail of the loaf but not the whole stack because that is already too far removed from the owner of the dog. ____________________________________________________________________________________________________________________________________ But then why would the dog with the loaf with a coal inside be not obligated? There is perhaps a possibility that it unusual act. A person lighting a fire is usual, but a dog is unusual. and a dog with a loaf is one more degree of separation. But then it would be second degree unusual. But why would that make any difference? צרורות are is obligated not because they are unusual. I think the רמב''ם in the case of the bucket with the chicken is going like the רא''ש (רבינו אשר)that force of force liable full damage but the case of the loaf is not force of a force but rather the רמב''ם is saying that ר' יוחנןand ריש לקיש are arguing about the reason for fire, but not about the law of the משנה. To ר' יוחנןif the dog put the loaf with the coal on the ערימה , it is liable for half damage; and ריש לקישsays if the dog did not put it down but rather carried it along the stack the liable only for the trail of the loaf but not the whole stack because that is already too far removed from the owner of the dog.