This is the passing action we added a while back. If you RMB close enough to a Bot indicated by your selector, you throw whatever you're holding to it and it catches it - or it throws what it's holding to you.
Here's one way to teach Bots how to throw to each other. The Bot on the left has been shown to find the nearest Bot in an area and 'add' to it (in this instance, the search area is a single cell, to guarantee which Bot is the target). It's as simple as that. You can build up silly sequences with Bots throwing things to each other now :D