The answer is relative to how large the phallus entering the anus is, compared to how often one engages in inter-anal intercourse. The sphincter is a muscle and can be conditioned to stretch if one partakes in too much anal sex.
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Your question is not specific but if you mean enlarge, it is not a good idea.
from baby gap
In the butt would most likely refer to anal sex.
None
Anal stimulation and pleasure.
Stick your fingers up your butt.
Rectum, Butt, or Bottom
no
It's the fin closest to the butt.
Yes, silkworms silk comes out of there anal opening-(there butt-hole)
The gluteal cleft, natal cleft or anal cleft