Or HaChaim on Exodus 21:33/אור החיים על שמות כ״א:ל״ג

1 וכי יפתח איש בור, If a man shall open a pit, etc. This means that even if an ox or donkey fell upon the person digging the pit, not only being killed itself but also killing the owner (digger) of the pit, the owner of the pit (or in this case his estate), must pay compensation to the owner of the animal which tripped and was killed although it caused the death of the owner of the pit (compare Erchin 7).