Understands, perhaps, vaguely the object is to get inside (10)

I believe the answer is:
apprehends
'understands' is the definition.
(apprehending is a kind of understanding)
'perhaps vaguely the object is to get inside' is the wordplay.
I cannot quite understand how this works, but
'object' could be 're' (Re is an example) and 're' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for apprehends that I've seen before include "arrests" , "Has a dread of" , "collars" , "Twigs" .)
