marbles

noun[plural only]3

1. •
   Any of several children's games played with small balls (made of marble or more commonly glass).

   • Egyptian boys played marbles before the days of Moses.
2. •
   (figurative) Sanity.

   • Grandpa's lost his marbles, but at least he still recognizes us.
   • Granny's still got all her marbles.
3. •
   Bits of rolled-up rubber shed by the tires of race cars that accumulate at the edges of the track, especially at the corners.

   • Some corners are littered with marbles, off the racing line. — 2014