Animal killing is not good. You never know when this brings what kind of calamity on the killer. There are a few examples in our scriptures where people had to suffer a lot for just hunting animals. These people had to suffer really a lot.
The first name comes to our mind is of Dasharath. Dasharath? Yes the same Dasharath who was the father of Raam. When he was young he learnt the art of Shabd Vedhee Baan (shooting the arrow at the sound). He used to go to forests and used to practice for it. Once he went to a forest, and was practicing his Shabd Vedhee Baan art. He heard a sound. He felt that it was a sound of an animal drinking water at a nearby river. So he shot his arrow to kill him. After shooting the arrow when he went to see his prey, he found that his prey was not an animal, it was a man who was filling water in his pot and that sound was not of the animal drinking water, but was of a man filling water in his pot.
When Dasharath reached there to see his prey he found the man at the point of dying. Raajaa got very sad seeing this. He asked the man - "Who are you and what are you doing here?" The man told him that he was Shravan Kumaar, His parents were blind, old and could not move themselves, so he was carrying them to Teerth (pilgrimage). They were feeling thirsty, so he came to this river to take water for them. They must be waiting for him. But since he was shot, he was at the point of death, he himself could not carry the water for them. Then he requested Raajaa to take water to them so that they could quench their thirst. He instructed him not to speak anything to them as they were very sensitive. They will recognize him soon." After having said this Shravan Kumaar died.
Raajaa took the water pot to Shravan's parents with a heavy heart. He gave that water to them. They said - "Son you got very late, we are waiting for you for quite a long time." When Dasharath did not speak for some time, they asked him - "You don't seem our son. Who are you who has brought water to us? Where is our dear son?" Dasharath had to tell them the whole story. Hearing the killing of their son, they got extremely sad and in spite of all kinds of assurance given by the King to them they could not be consoled. They cursed Dasharath - "We had nobody to take care of us, how we will live without him? We curse you that you will also die in the sorrow of the separation of your son as we are dying in the separation of our son." And they died.
For the same reason Raajaa Dasharath had to die when Raam went to forest for 14 years.
The second name is of his son Raam, who also had to suffer for the killing an animal. When Raam, Lakshman and Seetaa were spending their exile period in Panchvatee, once Seetaa saw a golden deer roaming around their Aashram. She liked the animal very much and could not resist Herself to get him dead or alive. She asked Raam to get him for Her. Raam knew everything - that there was no such kind of golden deer in the world, still He took up His bow and arrow and set off to catch him for Seetaa. Seeing Raam coming to himself, the deer started running from there. He took Raam very far deep inside in the forest. He was Maareech Raaakshas and came there to take Raam away from His Aashram according to Raavan's plan to abduct Seetaa. Raam was unable to catch him or kill him. But at one point He was able to shoot His arrow at him. The deer was about to die, so he showed his real form (of Maareech Raakshas) and cried in a loud voice - "Haa Lakshman, Haa Seetey".
Hearing these words Seetaa got restless and forced Lakshman to go help his brother. In spite of assuring Seetaa that nobody could harm Raam, Seetaa did not listen and asked Lakshman to go to Raam to help Him as soon as possible. Lakshman had to go and behind his back Raaavan abducted Seetaa. Everybody knows what had happened then. So even Raam had to suffer for just killing an animal.
The third example comes to our mind is of Raajaa Paandu in Dwaapar Yug. Paandu was also good at shooting Shabd Vedhee Baan. Once Paandu was living in a forest for enjoyment purpose with his two wives - Kuntee and Maadree. One day Maadree insisted him to kill a deer for her. Paandu took his bow and arrow and set off to kill a deer. After a while he heard some noise and he detected that that nose should be of a deer, so deciding this, he shot the arrow and the arrow hit the dear. When Paandu came to see his prey, he found that it was not a deer, it was a Rishi Kindam and Rishi and his wife were engaged in making love in the form of a deer.
Paandu also got very sad seeing this. He never thought of that he would kill a Rishi like that. Rishi and his wife were also very sad. The arrow was shot at the Rishi. He cursed Paandu to die in the same way when he would be engaged in making love. Thus he could not have any child of his own. After being cursed Paandu came back from there. Now he could not have any child of his own. He died, according to Rishi's curse, in the arms of his younger wife Maadree. Everybody knows that Kuntee helped him to have 5 grand sons from Dharm Raaj, Pavan Dev, Indra and Ashwinee Kumaar and brought them up alone. Maadree had become Satee with Paandu.
The fourth name is of Karn, also in Dwaapar Yug. Karn was also good in using Shabd Vedhee Baan. When he had learnt his archery, he also used to practice it in forests. Once he was practicing it, that his arrow hit a cow grazing in a field. Karn went to see his prey and found a cow killed from his arrow. The owner saw his cow dead and then saw Karn standing nearby with a bow. He got angry at this and said to him - "You princes think yourselves a very good archer and you don't know how to shoot an arrow. As you have killed my innocent cow, you will also be killed in a helpless situation." Karn asked him for his forgiveness but the owner was very sad at his cow's death, he could not be consoled. For the same reason Karn was also killed in a helpless situation.
These people had to suffer so much just for killing innocent animals. It is so sad.