They're slow-moving and hang upside down (6)
I believe the answer is:
sloths
'they're slow-moving and hang upside down' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for sloths that I've seen before include "Very slow-moving creatures" , "They're slow-moving and hang upside down" , "Slow-moving animals of tropical S America" , "Slow-moving mammals" .)