"The turtle eats an apple."

Translation: La tortuga come una manzana.

[BenBarth]

When do you know to use "un" rather than "una"

[Luis]

It depends on the grammatical gender of the word. Manzana is a feminine word, so you use "una"

[PadreStoningpot]

so if an animal has two forms would you use the male if gender of the animal is unknown, or do you go the the gender that best suits the animal? ie unknow sex dog perro unknown sex cat gata?

[cbreid]

In almost all cases, when an animal has both a masculine and feminine form and the gender of the animal in question is unknown, the default usage would be the masculine form i.e. "el gato" or "el perro". As with all things, there are a few exceptions which can be found in the links below.

http://www.duolingo.com/#/comment/88?from_skill=c337c97f80596bab031ffa0fa6cebf86
http://spanish.about.com/od/nouns/a/gender-animals.htm

[Michey2001]

I don't get the "se" before a verb like " se come"....when do we use se?

[AshutoshJam]

How can a turtle eat an apple

[KatnissStyles]

why would a turtle eat an apple? i don't get it

[Georgia315511]

not entirely sure