The pair was recently shooting a segment for the Tv crime drama's 100th episode with fellow castmate Ll Cool J when Olsen decided to take a hit from the taser for real - and was left nursing a nasty burn.
He explains, "There's a fight scene where (Ruah's) using a taser and she did it with Ll first, and he said, 'Don't turn it on', and... when she hit him with the taser, he acted. So when I show up a little bit later, I'm like, 'Yeah, let's put it on, let's do it for real.'
"It's one of those (stun guns) where you touch it once and it holds a charge, and if you continue to hold it down, it continues to send charges, so she hit me with it, with her finger on (the trigger) and it burned a hole in my arm. It's in the episode and it's very funny."
The anniversary episode airs in the U.S. on Tuesday night (15Oct13).
Ironically, Ruah is Olsen's soon-to-be sister-in-law - the actress is pregnant and engaged to marry Olsen's brother and Tv stunt double, David Olsen.