It's easier to use beagles. Pigs like to eat truffles, and they're damn smart and clever. They often sniff out the real thing, dig it out, then eat the truffle and then grunt and whine to their human owner, "no--I must have been mistaken--no truffle here after all." Dogs, in contrast, are perfectly willing to sniff out truffles for their human owners, but they have no interest in eating them. And dogs are too stupid to obfuscate, anyway.