"If enough get together they can swallow you whole." -RGBDoubts are normally seen as transparent and jellylike grey worms with no distinguishing features except for a mouth on one end and teeth lining the entire inside of the creature, suggesting the appearance of a lampry eel or perhaps a parasite. If ignored, they don't do much damage, and fight each other instead, however too many Doubts are capable of consuming a person, morphing together in order to form a solid "coating". It is also implied that they weaken Amour, as the Hero's coat seems to have turned into Doubts following the attack in The Plains of Hesitation.
They are encountered in the first part of the Hero's journey, while Hero and RGB rest beside the Pool of Tears. Hero attempts to throw one at a Fear, but it is sliced in half on the much sharper creature. Later, Doubts exacerbate the argument between RGB and Hero, and the two are able to re-unite once RGB rids himself of his and then saves her from being devoured by more.