more hash, array practice and multi line print with one statement

arr_1=["this", "that", "other", "and still, another"]
arr_2=[56, 9, "numbers", "creamy delights"]
test_hash_1={"stone"=>"agate", "animal"=>"capibarra"}

puts
puts test_hash_1
puts test_hash_1["stone"]
puts test_hash_1["animal"]
puts test_hash_1[arr_1] ### This should return an error, as I havent assigned a key to the value of 
### arr_1

puts
test_hash_2={3 => arr_1, 4 => arr_2, "animal" => "capibara", "stone" => "agate"}
puts
puts test_hash_2
puts test_hash_2["animal"]
puts test_hash_2["stone"]
puts test_hash_2[4]
puts test_hash_2[3]
puts
print <<eof
Apparently, a hash key can only be a number or a 
string, and not a letter variable, as letter variables 
return errors, while numbers and strings don't.

  And, it's worth mentioning, that this comment was printed 
  using the 'print <<eof' statement (function?).  'print <<eof'
  maintains formating, like the indent here.
eof