The context of the following conversation is Bailey was bit by spider on the arm so she killed the spider with a stone.:
Bailey says I was walking on the rocks and bent down to pick up one and the spider bit me on the arm..
The friend responds Did you see what kind it was?.
Bailey responds No, I picked up a stone and killed it before I could see..
The friend responds You should have left it alive, in case you have a reaction to the venom..