"Good girl, take another five points. So, whenever you need leaves or wood from a tree in which a Bowtruckle lodges, it is wise to have a gift of woodlice ready to distract or placate it. They may not look dangerous, but if angered they will try to gouge at human eyes with their fingers, which, as you can see, are very sharp and not at all desirable near the eyeballs. So if you'd like to gather closer, take a few woodlice and a Bowtruckle - I have enough here for one between three - you can study them more closely. ...
Harry Potter and the Order of the Phoenix
What does "for one between three" mean exactly? I can not figure it out.