Quotation from: The Adventures of Sherlock Holmes

Written by: Sir Arthur Conan Doyle

"You have an answer to everything. But how on earth do you deduce
that the gas is not laid on in his house?"

"One tallow stain, or even two, might come by chance; but when I
see no less than five, I think that there can be little doubt
that the individual must be brought into frequent contact with
burning tallow--walks upstairs at night probably with his hat in
one hand and a guttering candle in the other. Anyhow, he never
got tallow-stains from a gas-jet. Are you satisfied?"