The send and receive objects within the MIDI bpatcher had a strange arguments: #0-mono-poly. The # notation allows us to do some very neat things: #1 to #9 accesses the first nine arguments given to the patcher if loaded as an abstraction, and #0 provides us with a unique random number if the patcher is loaded as an abstraction. Open the Pound-Sign-Examples.maxpat patcher. It doesn't do a lot but simply loads the pound-sign-examples_abstr.maxpat abstraction. You can see both of them in the following screenshot. However, if you double-click on the abstraction to view its interior, you shouldn't see the same thing until you unlock the patcher. This is because until you unlock the patch, it is loaded as an abstraction and therefore all the # numbers are replaced.

So, that's pretty handy right? However, what do we need random numbers for? We often build abstractions with the aim of loading multiple instances of them. So, if we naively used [send] and [receive] without this notation...