Keeps going like a parasite (5,2)

'keeps' is the definition.
The answer and definition can be both to do with communicating as well as being verbs in their -s form.
Maybe they are linked in a way I don't understand?

'going like a parasite' is the wordplay.
I cannot really see how this works, but
'going' could be 'on' (both can mean functioning or activated) and 'on' is found within the answer.
'a' could be 'an' and 'an' is found within the answer.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?