One thing is, the feral cats have a certain tenseness and hyper-alertness. You can see that in Blondie’s body language. They are alert to EVERY sound and EVERY movement. And they are ready to run at any moment. To go from 0 to 50 mile-an-hour sprint in a split second. They often act as if warning alarms of DANGER DANGER DANGER are going off in their brains. The slightest sound will cause their head to instantly swivel in the direction of that sound. And they will stare intently off into space until they’ve concluded it was non-threatening.
Another thing is, they really are wild animals. You can actually see the wildness in Blondie’s eyes.