I don’t think it was from WB; more likely it was a Tex Avery product.
For some reason (maybe inheritance money), a guy is trying to kill a dog, I think. A bomb goes off or a shot rings out, and for a moment we think the poor thing is dead. Then the dog comes out dressed like Sherlock Holmes and reveals it was a dummy that was shot/blown up. In a British accent, he says “You were smart, _ _ _ _ _, but not enough to outsmart Scotland Yard!”
Ring any bells? :dubious: