What is the correct spelling "cats purr or purr"?
The cats are purring.
How do you write the test word?
Did the cat purr?
No, she purred ... and on one of the resources, full of knowledge, there is an article about cats, so there they follow the literary and spelling, and there cats purr.
The correct option is purring. The vowel in the personal ending of the verb (that is, in the ending of the present or future tense, in this case it is the 3rd person plural of the present tense) depends on the type of conjugation. For verbs of the first conjugation, this will be the ending -at (-yat), for verbs of the second conjugation, the ending -at (-yat) must be written.
The verb "purr" refers to the first conjugation, in this case it is determined by the infinitive ending in -at. This means that the ending of this verb in the form of the 3rd person, the plural of the present tense is -out.
One more form is acceptable - they purr. But this is not the main option, as well as forms of the type "waving" (colloquial), rinsing (colloquial), etc. According to the general tendency, all these forms are replaced by forms with alternating consonants: waving, rinsing, etc. This opinion is confirmed by the portal " Certificate of RU ".