lehanāmanthanākoṭaiḥ strīsukhasya bharāt smṛteḥ |
śaktyabhāve 'pi deveśi bhaved ānandasamplavaḥ || 70 ||

manthana [p= 787,2] [L=157572]
kindling fire by friction Nir. iii , 14
manthana [p= 787,2] [L=157573]
a churning-stick Hariv.
manthanī [p= 787,2] [L=157574]
a vessel for butter L.
manthana [p= 787,2] [L=157575]
the act of kindling fire by rubbing pieces of wood together ChUp. S3rS.
manthana [p= 787,2] [L=157576]
the act of shaking , shaking about , agitating , churning (milk into butter) MBh. Ka1v. Sus3r.
manthana [p= 787,2] [L=157577]
churning out (of amta) MBh. (cf. amta-m°).
(H2) mfn.
(H2B) m.
(H2B) f.
(H2B) n.
(H2B) n.
(H2B) n.

To get the sexual innuendo here, think about the circular motion of the penis in the vagina - look at Taoist or Tantric imagery.

Ariadne's Clue: A Guide to the Symbols of Humankind - Page 128
- 2001 - 480 pages - Preview
'The parmantha, or instrument of the manthana (fire-sacrifice), is conceived under a purely sexual aspect in India,' comments Jung. 'The fire-stick being the phallus or man, and the bored wood underneath the vulva or ...
Anthony Stevens

Cassell's encyclopedia of queer myth, symbol, and spirit: gay, ...
, David Hatfield Sparks, Mariya Sparks - 1997 - 382 pages - Snippet view
EROTICISM AND LOVEMAKING 134 people of Huichou referred to male same-sex coupling as "treading on tofu. ... including chatakavilasa, the "bird's amusement," alternately semi- penetrating and deeply penetrating the vagina, manthana, ...
Randy P. Conner

There is also the great myth:

Perspectives in the Vedic and the classical Sanskrit heritage
- 1995 - 275 pages - Snippet view
11 The Fourteen Gems in the Legend of Samudra-Manthana The legend of Samudra- manthana occurs in the MB (critical edition, Adi Parva, Chapters 15-17; SR, ...
G. V. Davane

Meditation: Any Time Any Where
- 2005 - 255 pages - Preview
The former was known as the Hridya Manthana Spanda and the later Brahma- Manthana Dharana. In Hridya Manthana Spanda the thoughts are emitted based on the impulses drawn from the heart. The emotions counted more rather than the brain ...
R. Venugopalam