Learn Spanish (Latin America): No tengo ni perro ni gato.

Spanish uses double negatives! If a negative word like ni comes after the verb, you must make the verb negative too by putting no in front of it. While in English you say 'I have neither...', in Spanish you literally say 'I do not have neither dog nor cat'.

Why isn't there a word for 'a' before perro and gato?

When using ni... ni... to list things you don't have, Spanish usually drops the indefinite articles (un or una). You just place the plain nouns right after ni.

Can I use a single ni instead of two?

Yes! While it is very common to see it doubled up as ni... ni... (neither... nor...), you can also use just one ni to mean 'nor'. You could say No tengo perro ni gato (I don't have a dog nor a cat).

What is the opposite of ni... ni...?

The opposite is o... o..., which means 'either... or...'. For example, if you wanted to say 'I have either a dog or a cat', you would drop the no and say Tengo o perro o gato.