"Transitional objects" as establishing operations for thumb sucking: a case study.

One preschooler who sucked his thumb only when holding a surgical cloth was watched at home and at preschool.

The cloth was taken away and returned several times. Staff wrote down every thumb-suck episode.

The child never sucked his thumb without the cloth. When the cloth was gone, the behavior stopped.

When the cloth came back, thumb-sucking started again. The cloth worked like a light switch.

Watson et al. (2002) saw the same thing with two siblings and a pillow. Taking the pillow away cut thumb-sucking in both kids, even the one who kept her pillow.

Sixties duckling studies (S et al. 1966, 1967, 1969) first showed odd items can control behavior. A plastic box made ducklings peck or eat only when it was near.

Storch et al. (2012) looked at object stereotypy and got mixed results. Their kids sometimes wanted control of the object, but the core idea matches: the item itself drives the behavior.

If a client carries a blanket, stuffed toy, or lucky shirt, try a quick test: remove it for one session. If the problem behavior fades, you have found a cheap, side-effect-free lever. No need to punish or reinforce; just manage the object.