Snakes! It has to be snakes. Here’s one from our book.

Delivery Snake

A result of careful breeding over many years, the delivery snake is large enough to allow a person to ride it or to hold several packages, and can be taught a route. This makes them superior to the previous breed, the homing snake, which had a strong instinct to return to its home. The delivery snake is remarkably fast for a snake, but the creature’s reflexes haven’t caught up with its improved speed, leading to occasional crashes into trees.

Attributes: Agility d6, Smarts d4 (A), Spirit d6, Strength d8, Vigor d8
Skills: Athletics d6, Fighting d4, Notice d10, Stealth d4
Pace: 8; Parry: 4; Toughness: 9
Edges: Fleet-Footed
Special Abilities:
Bite: Str.
Constrict: +2 to Athletics and Strength rolls made to grapple.
Crash-prone: When the snake moves more than 10” in a straight line, it moves the rest of its Pace (at least 1”) in a straight line, taking 2d4 damage if it crashes into something.
• Size 3: A delivery snake is 12’ long and is relatively thick for a snake (3’ in diameter).