This is something I ALWAYS do when watching a movie/TV even if I try not to. I'll be wathcing something and start thinking 'they look familiar', I've stopped telling my wife who they are when I figure it out as it just bugs her but Ive often spent half a movie (whilst still enjoying the movie) thinking "they were a younger sister or a cop or I remember them crying or something along those lines..."
Another one who does the sci fi rounds is the bearded actor from
Sliders, he played a holodeck historical person on voyager Davinci, I think? and I dont think he was the LOTR Dwarf but Im sure Ive seen him in something as a fantasy dwarf? and possibly in other sci fi shows...
Don't you see the actor who played Tuvok in Voyager in one of the earlier movies, I think he was a human and he was just a background character.
The monster from Young Frankenstein was Raymond's father in Everybody loves Raymond.
The principal in the Buffy series was the ferengie on DS9 and I think played a different one in the Next Gen episode when the Ferengie are first shown.
I can't remember the shows now but the actor who played Nelix in Voyager pops up every now and again.
but by far the silliest one I spent time trying to work out was Tim Roth in a monkey suit for the
Planet of the Apes remake. It was bugging me so much that I knew the voice and mannerisms that I looked at the cover but I couldn't place the name. About 3/4 of the way through the movie I jumped up and said that's the undercover cop from
Resevior Dogs
.... and got a roll of the eyes for a response