1) "The thing about theatre is that that performance is then gone" = Can I write "that" twice, one next to the other? yes, you can and often should. :) 2) "Dr Dolittle is not, of course, a real person, and authenticity is probably not the most important element in a story about talking animals" = I miss a "to" between "talking" and "animals"... As it is it means that the animals talk. They are talking animals. You could also change it to be about "talking to animals". 3) "It does my utter head in"... ¿some traslation in Spanish? It utterly does my head in. No obvious meaning for "utter head". 4) "Hence the increasingly great lengths actors go to in order to nail an accent down" Only a fragment of an idea. Hence .... Does not stand alone. But not incorrect. Audiences are now critical of poor accents, hence the increasingly great lengths actors go to in order to nail an accent down. BTW: no thanks comment necessary. Ask more, sure, but otherwise I just end up with lots of comments to check on. :) Several typos fixed. :(

because of that that is not going to happen

Ok Alberto, gracias! Esta oración estaba complicada pues comienza con el sujeto, había lugar a duda

2) No se refiere a hablar con animales, sino a animales parlantes/hablantes -> "talking animals"