Curtsy is an emote that was introduced on 7 October2009. This is one of the starting emotes and is available after the player unlocks emotes during the tutorial.
It is the default Bow option for female characters and the right-click option for male characters.
In the Circus, Bow and Curtsy count as the same emote.
If a Treasure Trail emote clue said to bow, it didn't matter if a player bowed or curtsied, since they count as the same emote. However, thanks to an update, clue scrolls will say "bow or curtsy" to combat this confusion.