Effect as described by Ian Adair: I remove a deck from its case and fan it front and back.
A spectator selects a card (any card) which is replaced. The deck is cut and shuffled.
I tell the audience that I forgot to bring out my pet mouse called Sniffy. I look inside the card case and there are squeaking noises coming from it. I then bring out a single card (same size as the other playing cards) which has a back design and on its front, a picture of my pet mouse.
I explain Sniffy is very good at ‘sniffing’ out chosen cards. The spectator is asked to rub the back of the chosen card which shows a triangular cheese portion ” This helps Sniffy find the cards much better. ” 
The card is replaced in the deck which is cut and then shuffled. The mouse card is placed on the top of the deck, picture side uppermost..then the deck is cut several times to lose it. Sniffy is on the run, looking for the chosen card!
When the deck is fanned, backs uppermost, it’s easy to find Sniffy amongst them..this is the only card which has its face upwards. The spectator is asked to remove the card which is next to Sniffy. When this is removed, it’s the chosen card. Clever mouse!

In another presentation, the deck is placed inside the case, and Sniffy finds the card ‘under-cover.' The audience can hear him squeaking – from inside the case ”Ah, he’s telling me it’s difficult to find the chosen card, but will do his best.” Deck is removed, and, as before the chosen card is found next to the mouse one.

The deck and mouse card can be left on the table and can be examined. The deck can also be used in other card tricks. We supply you with the 2 cards and the squeaker. You use your own (any poker size) deck.