Take part in an exchange of back mammal feet (4)

I believe the answer is:

swap

I'm a little stuck... Click here to teach me more about this clue!

'exchange of back mammal feet' is the definition.
'swap' can be an answer for 'exchange' (swap is a kind of exchange). I'm not certain of the 'of back mammal feet' bit.

I don't understand the rest of the clue.

Can you help me to learn more?

(Other definitions for swap that I've seen before include "Exchange; hands back" , "Exchange, barter" , "Change over" , "Wasp (anag)" , "Fifty-fifty odds" .)

I've seen this clue in the Sydney Morning Herald.

Want a hint initially instead of a full solution? Install my app