Running main.lua results in attempt to call method 'getAnimalId' (a nil value)

[tkafka]

$ lua main.lua

lua: main.lua:43: attempt to call method 'getAnimalId' (a nil value)
stack traceback:
    main.lua:43: in main chunk
    [C]: ?

In the end I gave up and tried http://lua-users.org/wiki/SimpleLuaClasses instead, that worked.