hat-trail and hat-observe errors

Hi, I'm getting some odd errors running hat under OS X.  I'm trying to 
work with a trivial piece of code to prove that hat is doing sensible 
things - which at the moment it isn't.  When running hat-trail or 
hat-observe I get the following error:

 > [host-172-17-2-19:Work/Project/test] tatd100% hat-trail stupid
 > sh: resize: command not found
 >
 > Fail: user error
 > Reason: Command (resize -u) failed

I originally assumed an incompatibility with my terminal (OS X's 
Terminal.app), but I receive the same error when using xterm (under 
Apple's X11 server).  I've been searching source files for where they 
might call the resize command, but can't find it.  Any help much 
appreciated.

Thanks

Tom Davie