Animals:

They usually ride high tharlarions (nc7). Tarns would not be likely (nc35), but not out of the question (nc1, nc39 ). Assassins can use sleen to track but should not use them for kills as it breaks the code (nc45), although the group of 22 assassins intended to as a last resort (nc73).

(notecard nc35 of Garians original SL Gor document)
I had decided to wait until the Fourth Passage Hand, that following Eh'Var, and then take tarn for Ar, where I would pose as a mercenary tarnsman seeking employment in the House of Cernus, but when the Warrior from Thentis, who resembled me, was slain early in En'Var, I decided to go to Ar in the guise of an Assassin, by High Tharlarion, for Assassins are not commonly tarnsmen.
Assassin Of Gor, Chapter 5

(notecard nc1 of Garians original SL Gor document)
Our discussion terminated abruptly. There was a rush of wings outside
the window of my apartment, and the Older Tarl flung himself across the room and dragged me to the floor. At the same moment the iron bolt of a crossbow, fired through one the narrow windows, struck the wall behind my chair-stone and ricocheted viciously about the room. I caught a glimpse of a black helmet through the port as a warrior, still clutcing a crossbow andmounted on his tarn, hauled up on the one-strap and flew from the window.
    There were shouts, and, rushing to the window, I saw several answering bolts leave the cylinder and fly in the direction of the retreating assailant, who was now almost half a pasang away and making good his escape.
    'A member of the Caste of Assassins,' said the Older Tarl, gazing at the retreating speck in the distance. 'Marlenus, who would be Ubar of all Gor, knows of your existence.'
Tarnsman Of Gor, Chapter 4

(notecard nc39 of Garians original SL Gor document)
I thought for a moment. Some Assassins are, as a matter of fact, skilled tarnsmen. "Yes," I said, "I am familiar with tarns."
Assassin Of Gor, Chapter 13

(notecard nc45 of Garians original SL Gor document)
In Thentis, for example, sleen are used to smell out contraband, in the form of the unauthorized egress of the beans for black wine from the Thentian territories. They are sometimes, too, used by assassins, though the caste of assassins itself, by their caste codes, precludes their usage; the member of the caste of assassins must make his own kill; it is in their codes.
Slave Girl Of Gor, Chapter 8