Where did the r’s go?

An answer from my ass to S who wants to know:

“If you remove the “r” in the danish word for ass, “røv”, you get “øv” which could mean “damn”, “argh!! or “practice” (imperative form) in english. But where does the “r” go when an ass says “øv”? And why do so many danish people forget about the “r” at the end of present tense verb and where does the “r” disappear to when they forget?
Your friend always,
S