Werewolf Appearance

[mullsym255]

No: HPFGUIDX 32407

I'm sorry if this has been discussed before (I did a search and 
nothing came up), but just what does a werewolf look like when it 
transforms? I've obviously seen various different versions in movies, 
and most seem to show that a werewolf is essentially a wolfish man 
(ie walks upright on two feet). But is this what were supposed to 
believe Lupin looks like? I seem to think that we're supposed to 
believe he looks like a real wolf (ie walking on all fours). 
Especially from that clue that he's able to "curl up" in his office 
after taking the wolfsbane potion. Perhaps we're just suppose to 
picture him however we want to. How has everyone else pictured Lupin 
after transformation?