According to the Mishna, if someone places his fruit in someone else’s yard without his permission, the owner of the yard will not be responsible if his animal eats the fruit; if the animal is injured by the fruit then the owner of the fruit will be liable for damage done to the animal.
In the Gemara, Rav argues that the owner of the fruit will only be held liable if the animal tripped on the fruit or slipped on them. If he was injured by eating them, however, the owner of the fruit will not be held liable since the animal should not have eaten them (i.e. the animal itself caused the damage by eating). The Gemara quotes a baraita that teaches a similar rule with regard to someone who places poison somewhere that his friend’s animal eats it – he will not be held liable to pay, even though he will be held responsible in the heavenly court (hayyav be-dinei shamayim). The Gemara explains that with regard to fruit that an animal normally eats this is true, but that even in the case of poison – something that an animal does not normally eat – the person who placed it there will be hayyav be-dinei shamayim.
Most animal are sensitive to poisons and avoid eating them, both because they are not their normal food and because they succeed in recognizing them, probably by means of their sense of smell. Similarly, animals ordinarily do not eat poisonous plants. Nevertheless there are times when an animal will eat a plant that it does not recognize as poisonous, either because the poison comes from germs on the plant rather than the plant itself, or because it does not have an offensive smell. This sometimes leads to an animal eating plants that can cause them illness or even death.