What's going on here?

gistfile1.rb

begin
  puts foo.inspect  # This raises an exception
rescue
  puts $!.message
end

if false
  foo = 100
else
  puts foo.inspect  # This raises nothing (even without the above begin..rescue block)
end

# Or even:

if false
  goo = 100
end
puts goo.inspect

# But it does raise if the if..else order is reversed 
if true
  puts bar.inspect
else
  bar = 100
end

# $ ruby foo.rb
# undefined local variable or method `foo' for main:Object
# nil
# nil
# undefined local variable or method `bar' for main:Object