A natural way would be to crack open 9-10 morello cherries, extract the kernels from the cracked stones, chew them extremely thoroughly and finally swallow. As with apricot kernels, where you need around 20 kernels, you will sense an almond-like flavor, which is due to the cyanide precursor amygdalin from the chewed extracted kernel seed being converted to HCN and benzaldehyde by enzymes in the saliva, the flavor coming from the benzaldehyde. So you create your own cyanide poison for your CTB. I tried 3 plum stones and detected that flavor, but many more plum kernels are needed for any chance of a successful CTB.
You may consider combining this technique with use of other substances, chemicals, drugs, alcohol, etc., as long as they do not interfere as techniques with each other, in order to be more sure of getting successful CTB.
Red cherry pits contain 3.9 mg/g of amygdalin, black pits contain 2.7 mg/g, while morello cherry seeds excel with 65 mg/g. The lethal threshold for ingested amygdalin is between 9 and 60 mg per kg of body weight for the average adult. With cherry pits weighing around 1 gram, a 150-lb person needs to ingest at minimum 612 mg of amygdalin to get a lethal dose of cyanide. That means 157 red, 227 black, and 9 morello cherry pits.
The seeds inside apricots, peaches, apples, plums, and almonds all contain significant amounts of amygdalin, but morello cherry kernels seem to be really efficient for CTB. Of course, the lethal number of kernels should be chewed as fast as possible, but thoroughly, so the body does not have time to remove the cyanide fast enough to prevent CTB.