Elixir: what is a cat?

I like cats, but what are they made of?

Robs-iMac:hello roblacey$ iex
Erlang/OTP 21 [erts-10.2.1] [source] [64-bit] [smp:8:8] [ds:8:8:10] [async-threads:1] [hipe] [dtrace]

Interactive Elixir (1.7.4) - press Ctrl+C to exit (type h() ENTER for help)
iex(1)> 'cat'
'cat'
iex(2)> Enum.to_list 'cat'
'cat'
iex(3)> [head | tail] = 'cat'
'cat'
iex(4)> head
99
iex(5)> tail
'at'

Ok, so Single-quoted strings are really lists of characters. Double-quoted strings are not.

iex(6)> Enum.to_list "cat"   
** (Protocol.UndefinedError) protocol Enumerable not implemented for "cat"
    (elixir) lib/enum.ex:1: Enumerable.impl_for!/1
    (elixir) lib/enum.ex:141: Enumerable.reduce/3
    (elixir) lib/enum.ex:2979: Enum.reverse/1
    (elixir) lib/enum.ex:2613: Enum.to_list/1