When dirt gets into the trackball area, it can cause the mouse to skip around the screen, slow down or not move with fluidity. Cleaning the trackball will often correct common mouse problems.
To clean the mouse:
1) On the bottom of the mouse, turn the plastic "O" ring counterclockwise that holds the mouse ball in place and remove.
2) Remove the ball from the socket and try blowing some compressed air into the socket to remove dust particles.
3) Clean the roller connectors in the socket with a small amount of Isopropyl alcohol on a cotton swab.
4) Cleaning the mouse will normally correct the "sticking" problems that you may encounter.