The meaning of つま先を突っ張らせて in this context (describes a person's toes)


I met this expression in an eroge, but find it's hard to understand. My guess
is "Her toes were constricted "( ? ) but i'm not sure.

> 荒い吐息に合わせて浅く浮き沈みしていた下腹部を、内側から撫であげてやると、ティーナはつま先を突っ張らせて腰を跳ねさせた。

Context is a H-scene, where the protagonist

> used his middle finger to fingering a girl's vagina.




In terms of the meaning, the latter part of the sentence means she feels
sexual orgasm. Cf. [足ピン](https://dic.pixiv.net/a/%E8%B6%B3%E3%83%94%E3%83%B3)

About more language side of it, 突っ張る means _to stretch out_. A similar usage
is 顔(or 肌)が突っ張る, which means _to feel stiffness on your face/skin_. So
つま先が突っ張る is similar to cramp.

腰をはねさせた is (a variation of) another stereotypical expression for orgasm,
meaning moving up the waist instantly (I suppose it is described more
standardly as 腰を浮かせる).

