That's a good question, and it really boils down to personal style. 

My preference for passing arguments to `sleep` is that if you're specifying an integer you can drop the parentheses:

``` ruby
sleep 5
```

But if you're passing a variable you should use parentheses: 

``` ruby
# Looks reasonable
sleep(interval)

# Looks weird
sleep interval
```

I read up on this a little more, and [this post](http://blog.mojotech.com/post/31812700196/a-fireside-chat-about-optional-parentheses) makes the argument: 

> Parentheses should indicate that you are treating the method invocation as an expression, even if you aren’t assigning its value.

In which case, you're right, I should drop the parentheses and be consistent with the rest of the code base. :smile: