Hide
hide ei
This hides the specified image

Its only useful for changing facial expressions (especially ones that change the characters silhouette, as the previous picture will be visible underneath)
It is also useful for a character leaving by themselves without ending the scene) 

play music
play music "music/Poem1.ogg"
This plays the music file

noloop
play music "music/Poem1.ogg" noloop
This plays the music file without looping

pause

pause 42
This pauses all dialogue for 42 seconds, in this time, players should not be able to skip

This should not effect music or images 
(though of course music and images only change based on dialogue advancement)