Have you seen the movie "Training Day?"?

Question

There is a scene where Denzel Washington tells Ethan Hawke a riddle about a snail when they are at that guy's house that is later murdered. He says something about the snail knocks on some guy's door and the guy picks him up and throws him. After a long time the snail comes back and the guy asks the snail why he came back. Denzel tells Ethan when he figures out that riddle he will know the streets. What does this riddle mean?

Answer 1

It probably means the people in the streets, including cops, are weak and powerless like snails to prevent crime and corruption. Crime and corruption on the streets is a force of it's own and you are as powerful as a snail when you try to confront it, let along try to rid it. It might also mean there are people more powerful than the two cops, who really control the streets for their own illegitimate gain, and they treat them like snails -- toss them out when they get in the way.

Answer 2

It's a metaphor. The Eurythmics said it best - "Some of them want to use you, some of them want to be used by you. Some of them want to abuse you, some of them want to be abused."
The snail is the drug user, streetwalker, etc, and the man is the drug dealer, pimp, etc.
See the text below for the actual text (couresty of http://sfy.ru/sfy.html?script=training_day):
ROGER
Here's a joke, boy. One day this
man walks out of his house to go
to work. He sees this snail on
his porch. So he picks it up and
chucks it over his roof, into the
back yard. Snail bounces off a
rock, cracks its shell all to
s**t, and lands in the grass.
Snail lies there dying.
A BEEPER BEEPS. Roger checks and ignores it.
ROGER
But it doesn't die. It eats some
grass. Slowly heals. Grows a new
shell. And after a while it can
crawl again. One day the snail up
and heads back to the front of the
house. Finally, after a year, the
little guy crawls back on the
porch. Right then, the man walks
out to go to work and sees this
snail again. So he says to it,
'What the f**k's your problem?'
ROGER
Figure that joke out and you'll
figure the streets out.

Answer 3

Things always come back to bite you in the a**

Answer 4

yeah, it was a pretty good movie