Whisper bulbs (also affectionally known as "screamers" in windier locales) are sentient plant-animal hybrids that eventually emerge from trees pollinated by The Whisperer. Whispers are also capable of reproducing by infecting the tree with a virus that spreads to other locations in the tree, and may sometimes spread to nearby trees using crosspollination.

Although whispers are immobile and cannot hunt, they are capable of tapping the tree they've grown out of for nutrients. Left alone, whispers generally match the lifespan of the tree they depend on, although too many whispers absorbing nutrients from a single tree may kill it.

The shape of a whisper produces a distinct, high-pitched whistle when wind passes through it, increasing in decibels as the speed of the wind increases.