Acts like a predatory cat, eating small sweets? (7)

'sweets?' is the definition.
(mousse is a kind of sweet)

'acts like a predatory cat eating small' is the wordplay.
'acts like a predatory cat' becomes 'mouses' ('to mouse' can mean to hunt for mice).
'eating' means one lot of letters goes inside another.
'small' becomes 's' (abbreviation - e.g. clothes size).
'mouses' enclosing 's' is 'MOUSSES'.