Leaves one's bed to grab a bit of supper (4,2)
I believe the answer is:
gets up
'leaves one's bed' is the definition.
The answer and definition can be both related to thinking as well as being verbs in their -s form.
Maybe they are linked in a way I don't understand?
'to grab a bit of supper' is the wordplay.
'to' becomes 'getup' (I can't justify this - if you can you should believe this answer much more).
'grab' means one lot of letters goes inside another.
'a bit of' suggests taking the first letters.
The initial letter of 'supper' is 's'.
'getup' going around 's' is 'GETS UP'.
Can you help me to learn more?
(Another definition for gets up that I've seen is " Raises oneself from bed".)