I usually say something along the lines of: A novel environment, tons of stimuli, and lack of social interaction are among the factors that cause dogs stress when entering a shelter. (patriciamcconnell.com)
Most children aren't taught how to interpret dog stress signals, and short classes on these signals can prevent them from being bitten or otherwise injured. (ccpdt.org)
So you grasp what makes dogs stressed during grooming: a mix of noise, vibration, and all of that very close to their body and head. (breedingbusiness.com)