Reptile runs under a log, tail swishing (9)
I believe the answer is:
alligator
'reptile' is the definition.
(alligator is a kind of reptile)
'runs under a log tail swishing' is the wordplay.
'runs' indicates an anagram.
'under' says to put letters next to each other.
'swishing' becomes 'r' (I am not sure about this - if you are sure you should believe this answer much more).
'a'+'log'='alog'
'alog' next to 'tail' is 'alogtail'.
'alogtail' is an anagram of 'alligato'.
'alligato'+'r'='ALLIGATOR'
Can you help me to learn more?
(Other definitions for alligator that I've seen before include "Large carnivorous reptile" , "It could be in zoo" , "predator" , "Amphibious reptile" , "Vicious attacker" .)