Original: Thus pain and pleasure act as checks on each other : '' To gain a desired prey , a dog or wolf will do things that , in other contexts , they would shy away from : run through thorn bushes , jump into cold water and expose themselves to risks which would normally frighten them .
Simplified: '' To gain a desired prey , a dog or wolf will do things ( that they would normally not do , such as ) run through thorn bushes , jump into cold water and expose themselves to risks which would normally frighten them .