Again, the anti static brush helps as well as the computer spray. It happens to us all. Mud, sand, water or rocks. They all hurt photo gear. Rolls of film love water holes and spaces under rocks.
Cameras like to fall on exposed lenses.
Shaking a bit or tapping on hand or leg will knock off some stuff. Wiping with a damp cloth will get a lot of mud. Force will cause more problems. Having all your gear clean before going into the field helps a lot. It also gets you familiar with all of it.