Thumb twiddling is an activity that is done with the hands of an individual whereby the fingers are interlocked and the thumbs circle around a common focal point, usually in the middle of the distance between the two thumbs.

While it is an expression of at least a moderate amount of manual dexterity, thumb twiddling is frequently used as an example of a useless, time-wasting activity. It is equated with other activities that are also considered useless by the speaker. Therefore it is most often used as a synonym for an activity that will take the attention of the performer, but will not yield any useful results.

Thumb twiddling can be seen as an expression of which hand is dominant within the individual. The weaker handed thumb will "follow" the dominant handed thumb in the activity.

Variations

Two major differences between how people twiddle their thumbs involves whether or not the thumbs touch each other during the activity. Most frequently, the thumbs rotate around a common axis with a small space separating them of anywhere between 1/16th to 1/4 of an inch. However, a non-trivial number of people twiddle their thumbs where they continually touch each other, most often at the last knuckle, but sometimes touching at the first knuckle.

Another variation, which is very infrequently used, is for two people to participate in the activity, one contributing the left hand, and the other the right hand.

Obsessive-compulsive behavior

Thumb twiddling can start out as an innocent activity, but can become a problem if the individual performs this activity to excess. Excessive demonstration of this activity may, actually, be evidence of a mental, or neurological, problem. Excessive thumb twiddling may be one of many symptoms of an obsessive-compulsive disorder.

Medical uses

Asking an individual to twiddle their thumbs can be used as a simple test for manual dexterity.