An on-the-spot warning to 'watch it' (4,4)
I believe the answer is:
look here
But I can't explain it at all! Could you help me understand?
(Other definitions for look here that I've seen before include "See this; angry response" , "call for attention" , "Heed me now!" , "calling for attention" , "Exclamation of protest - gaze at this place" .)