A Castle and a Cat

Where is my spot ?

Yes, they're on leash.  But why ?
Imagine a nice open and sunny field with a tiny white spot
right in the middle of it...
Then take Charlie (off-leash) who spotted the spot and ran, and ran and ran...

What are masters supposed to do in that case ?

WAIT...
And WAIT...
And WAIT....

The spot ended all right.
Charlie ended on leash.
And we ended with painful and stretched arms...

PS : As many whippet owners must have guessed, the spot was a deliciously fluffy cat.