What does "bent in upon its body" mean?

Question

At once, the spider's leg bent in upon its body; it rolled over and began to twitch horribly, rocking from side to side.

I don't understand the phrase "bent in upon". I can't picture what it would be like when the spider's leg bent in upon its body. What's the correct way to understand it?

Quoted from Harry Potter and the Goblet of Fire.

Answer 1

One of "bend" verb meaning is (past tense and past participle bent):

to move part of your body so that it is not straight or so that you are not upright

So, when the spider's leg bent in upon (on) its body, it may mean its leg bent inside its body, on its abdomen.