What 5 letter word, when all capitilized, reads the same way upside down?

Question

I saw this interesting brainteaser and couldn't figure it out. Can anybody come up with a word that works?

Answer 1

I don't know, but would it have to consist of "H", "I", "O", or "X" to be read the same way upside dowm?  

Answer 2

SWIMS