show() effects, some working, some not

show() effects, some working, some not

I've got an image tag like so:
  1. <img id="hello" src="hello.png" />
and if I try to .show() it with certain effects, it won't work.

For example, $('#hello').show("bounce") works, while $('#hello').show("drop") doesn't.  A number of other effects won't work either (while some others do).

What am I missing here? I've got the proper jQuery 1.4 and jQuery UI 1.8 includes, and jQuery UI CSS stylesheets in place.  I'm stumped...