Ring a bell - or shout a warning (4,2,4)
I believe the answer is:
call to mind
'ring' is the definition.
The answer and definition can be both to do with communicating as well as being verbs in their base form.
Maybe there's an association between them I don't understand?
'a bell or shout a warning' is the wordplay.
I cannot really understand how this works, but
'a' is within the answer.
'bell' could be 'tom' (I've seen this before) and 'tom' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for call to mind that I've seen before include "Recollect" , "Remember" , "Cause to be remembered" .)