adding new objects?

I am trying to make an animation where one stick person shoots another stick person and blood spurts out.
However when I try to add the blood into the animation it shows it as if the blood has been on the guy since the beginning.
How can I make it so the blood doesn’t show up until the guy gets shot:?:

You can set the amount parameter to 0 making it invisible, actually transparent, and setting the amount back to 1 again when you need it.

How do you change the parameter?

In the ‘Params’ menu there is summary of the things that can be changed about the selected object (so, before going there, select the object you want to make invisible or do it now). One of the things you can change is the ‘Amount’. If you (double)click on the number behind that, you will be able to change that number. Set this to ‘0’ (zero) to make the layer invisible and change it to ‘1’ (one) to make it fully visible again. Everything between zero and one will make the object partially (in)visible.