Śatapatha Brāhmaṇa ("of a hundred paths") 4.6.9.6

4.6.9.6

tasya parastādevāgre 'lpaśa iva prāśnāti | tadenadupanimadati tadveda na vai tathābhūdyathāmaṃsi na vai māhiṃsīditi tadenamupāvaśrayate sa ha priya evānnasyānnādo bhavati ya evaṃ vidvānetasya vrataṃ śaknoti caritum

He first eats a very little from the further (back) end of it;--thereby he encourages it: it knows, 'It was not so as I thought: he has in no wise hurt me.' Thus it becomes attached to him, and, indeed, whosoever, knowing this, is able to observe the vow thereof, he becomes an eater of food, dear to food.