Learn Turkish: Kediye çok kötü davranıyorlar. - They behave very badly towards the cat.

The verb davranmak (to behave or treat) requires the dative case for whoever is receiving the action. In English we say 'they treat the cat', but Turkish thinks of it as 'they behave towards the cat'. So we add the dative suffix -e to kedi.

Why is there a 'y' in kediye?

Kedi ends in a vowel, and the dative suffix is also a vowel (-e). Turkish uses the buffer letter y to separate two vowels, so we get kedi + y + e.

If kötü means 'bad', how do we know it means 'badly' in this sentence?

In Turkish, you don't usually need a special ending (like '-ly' in English) to turn an adjective into an adverb. Because kötü is placed right before the verb to describe how they are behaving, it naturally functions as 'badly' in this context.

Can davranıyorlar mean 'they are treating' as well as 'they are behaving'?

Yes! Davranmak means both 'to behave' and 'to treat'. When used with a dative object like kediye, it is often best translated into English as treating someone or something a certain way.