Why couldn’t the man open the door?

My friend Tom kepi birds. One day he phoned and told me he was going away for a week. He asked me to feed the birds for him and said that he would leave the key to his from door in my mailbox.
   Unfortunately, I forgot all about the birds until the night before Tom was going to return. What was worse, it was already dark when I arrived at his house. I soon found the key Tom gave me could not unlock either the front door or the back door. I was getting desperate. I kept thinking of what Tom would say when he came back.
   I was just going to give up when I noticed that one bedroom window was slightly open. I found a barrel and pushed it under the window. As the barrel was very heavy, I made a lot of noise. But in the end, I managed to climb up and open the window.
   I actually had one leg inside the bedroom when I suddenly realized that someone was shining a torch up at me. I looked down and saw a policeman and an old lady, one of Tom’s neighbors. "What are you doing up there?" said the policeman. Feeling like a complete fool, I replied, "I was just going to feed Tom’s birds."