It is said that while Bagon wish for wings, Wooper wish for arms, and through evolution both of these dreams have come true. A Quagsire's arms are not the most useful appendages - they are short, lack thumbs, and are as much flippers for swimming as tools for manipulating objects – but for Wooper used to using only their tail, they are more than enough.
It is commonly believed that Quagsire are so happy to have arms at long last that nothing can bring them sorrow. This is quite possibly a myth; Wooper themselves are far from being a sad pokemon.. But it is easy to see how this misconception developed, for Quagsire are a tough species of pokemon which shrug off being struck by lightning, fight their battles without a grimace when hit by all except grass attacks, and their mouth seems to be in a perpetual smile even wider than Wooper's.
The slime surrounding its body, not the arms, is believed by many researchers to be the cause of this happiness. Unlike Wooper's toxic film, Quagsire slime has long been a popular recreational drug and has recently been approved to treat depression. When overdosed on, it can have a negative effect on intelligence and cause the body to be slow to react to dangers, symptoms also seen in virtually all Quagsire. Quagsire do, however, become happier when given large objects to manipulate, and in the rare cases where their arms are lost in an accident, they seem to live in perpetual mourning, taking it harder than even pokemon which rely on their arms to attack.
Regardless of the reason, Quagsire smile even more than Wooper, for they are even happier.