Yes it can be used on almost anything. I'm thinking you need feeling behind a spell
Originally Posted by erock98
Adding to this, Bellatrix also said to Harry right after Sirius dies (even though he did not die! ) that you have to mean a spell to want it to work. If you don't really mean the spell, then it won't work how you want it to. With Expelliarmus, you would have to mean for the spell to cast someone off their feet, just as Snape probably wanted to do to Lockhart to embarress him . Harry, though, didn't want to knock Snape backwards, he just wanted to disarm him so he can get to Sirius instead. He didn't know that Ron and Hermione thought the same thing, and thus, even if not wanting to, the three spells worked the same as Snapes' one spell against Lockhart.
Did that make any sense?