(Book 5: Sundara Kaand`a - Book of Beauty)
Gaja indra hasta pratimaha ca piinaha
Tayooho dvayoooho samhatayooho sujaataha
PraspandamaanaH punaha uuruhu asyaa
Raamam purastaat sthitam aacacakshee.
Context: Sita was in the As`ooka Garden. Stolen by Ravana, she was under confinement. She was in a miserable condition, threatened by Ravana. At that time Hanuman appears before her and consoles her. This verse is a foreboding of good things to come. She gets good omens such as quivering of left eye and left thigh.
Meaning: Sita saw many good omens. Her left thigh started quivering (praspandamaanaha). (A belief of those days that quivering of left parts in women, brings good for them, we do not bother today). It spoke (aacacakshee) as though Rama was in front of her (purastaat sthitam). Valmiki described her thighs as strong, comparing them to the heads of princely elephants (Gajeendra hasta pratimaha ca piinaha) .
Pl. see Review No. 28 at this blog. There you can find that Valmiki (through Rama) described Sita's thighs as resembling the trunk of a Kakubha Tree.