The hints below get progressively more specific. (Select the text to see it).
You might not yet have everything you need.
You need something to make yourself froth at the mouth.
Bosco's store back on the street might have something.
The shaving cream could work, but the rats take it!
You'll have to chase the rats in your car.
You need to get the rats to crash.
Shoot on the left or right side of the rats to force them to move.
Force the rats to drive into the open manhole.
Now go back to the studio and use the shaving cream.
When the director asks you to be rabid, use the shaving cream on yourself.