Tsientsien Don't Eat (Planetary Crossings Part I)

The following is a classic altered, then updated by me. The original mentioned multicellular "Martian" life. Since it is unlikely that there is much of anything beyond bacteria analogues on Mars, and maybe not even that, I have used the very possibly habitable Kepler-186f instead:

Jonathan Mark gathered three specimens of Keplerian plant and animal life to bring back to Earth: a garble, a farfel and a tsientsien. But Mark was worried. His vehicle for local travel was not big enough to hold more than himself and one specimen. Mark knew that garbles will eat farfels if given half a chance, and farfels will eat tsientsien. Garbles, however, don't eat tsientsien, and tsientsien don't eat. All the other astronauts were away from the ship. How could Mark transport the garble, the farfel and the tsientsien one at a time so that they would all be safe?

(Source: Fantastic Book of Logic Puzzles by Muriel Mandell, illustrated by Elise Chanowitz)

If this sounds familiar, maybe it should. My earliest memory of the same is one with a wolf, a goat and a cabbage. These things go back a long time. Here it looks like some oddly named secondary consumer will eat a primary consumer, if left alone with it, but not a primary producer. The primary consumer will however eat the primary producer if the two are left alone. (Remember, the latter likely has no voice. Or, maybe? It's the Kepler-186 system after all.) Anyway, how to get these creatures over the river?

The first step is to realize that there is only one first step: taking the farfel over to the far bank of the river, leaving behind a dangerous secondary consumer but with something he or she or whatever pronoun fits would not want to eat anyhow.

Now, with the farfel on one side of the river, returning to the other side, there are the garble and the tsientsien. Taking the garble over would result in the garble and the farfel on the other side of the river alone in the next step, which is impermissible. The only choice is then to take over the tsientsien.

What this results in is the farfel and the tsientsien on the same side of the river, which is bad. However, the key to solving this problem is backtracking: bringing what was once brought to the far side back to the near side. Because the tsientsien was just brought over, it seems like doing this will just undo progress. So take the farfel back.

Now the garble and the farfel are on the near side. Also not good. But now the garble can be taken to the far side, where ... it? ... will not eat the tsientsien. Lastly a trip back to the near side and back again will bring the farfel over, placing all organisms on the far side.