28 across
Extremely
short
experiment
on
rat
(7)
Extremely short experiment on rat (7)
hints
0
checks
0
hints
The definition is at the beginning of the clue.
How the clue works
The definition is extremely short — CURTEST means most curt. For the wordplay, rat gives you CUR (a contemptible mongrel), and experiment gives you TEST, with "on" just stitching the two parts together.