Curl up or flatten (4)
I believe the answer is:
roll
I believe this is a double definition.
'curl up' is the first definition.
(I've seen this in another clue)
'flatten' is the second definition.
(rolling is a kind of flattening)
'or' acts as a link.
(Other definitions for roll that I've seen before include "Drumming pattern" , "Drums sound" , "Barm cake" , "Cylinder (of paper etc)" , "Small rounded bread" .)