[Rails] Calling a function: one space difference between failing and succeeding

I have a function defined as follows:

def download_file (url1, url2, file1, file_age_max_hours)
    puts (url1)
    puts (url2)
    puts (file1)
    puts (file_age_max_hours)
end

The following command works:
download_file("Hello", "World", "Rubyists", 34)

The following command fails:
download_file ("Hello", "World", "Rubyists", 34)

The only difference is the space before the "(".  Why is the presence or absence of this space so significant?  This was never a problem for me in Python.  (On the other hand, I quickly learned to NEVER use tabs to indent when programming in Python.)

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