A few other helpful tools are:

  require 'tracer'; Tracer.on

That works a lot, but in some cases it can get caught in a loop where it doesn't print the trace. When that happens, or if I want to just see method calls, etc. I'll use a tool I wrote called autolog:

  gem install autolog

Then in the code:

  autolog do
    # some code
  end

Autolog is basically a quick and hopefully more intuitive way of using Ruby's set_trace_func. If all of those don't work, I've listed a few other options in the README that others have mentioned: https://github.com/garysweaver/autolog