Complex sentence: Because Gaz is very rarely ever seen to be happy most viewers believe that she is humorless, but in the episode "Parent Teacher Night" she chuckles twice at Zim and Dib's misfortunes.
Split into simpler sentences: Because Gaz is very rarely ever seen to be happy, most viewers believe that she is humorless. But in the episode "Parent Teacher Night" she chuckles twice at Zim and Dib's misfortunes.