That is a limerick by Edward Lear, 1812-1888, who popularized the verse form. He is considered one of the masters of "nonsense verse," and it appeared originally in a book whose title was "A Book of Nonsense." That tells you not to try too hard to understand the meaning. The meaning is that the man was sleeping. He thought his street door--the main door leading to the outside--was closed. If it had been closed, he would have been fairly safe from the rats. It would have been difficult for them to get in. He was wrong. It was open. So, some "very large rats" got in, and "ate his coats and his hats." More likely they would have stolen food from the kitchen. The humor is subtle. It is very cultural. It is a matter of word sounds, gentle incongruities, and "tone of voice." And I have to say that Lear's limericks, like this one, are very subtle. A lot of people wouldn't think it was funny at all. "Limerick" is the name of a town in Ireland and it's pronounced as three syllables, lim-a-rick. Lear did not call his verses "limericks" and there's no convincing explanation of how they got that name. I think you need to know that "dirty limericks" are very common. There is a whole folk subculture of limericks that are crude jokes on the topic of sex. I can't possibly post any examples. I think it's fun to make up limericks. There once was a man from Milwaukee Whose humor was terribly pawky. He couldn't tell jokes That were pleasing to folks So he posted them all to italki.

This is a limerick. It's a humorous kind of poem which has a special rhythm. Reciting limericks is a good method for improving pronunciation, particularly intonation. The words of most limericks (including this one) are normally stupid and do not deserve analysis. All the words in this limerick have their ordinary dictionary meanings.