Question: What exactly did Shane do to Bernie?
Question: What does the Lion mean that "humans can't handle it" if they do break the code to talk to them?
Answer: Most likely that learning that animals could always talk would be a big shock to them and they wouldn't know how to handle it.
What they're (Humans) gonna do if they can't?
When a "reality that has always been true" (animals can't talk) turns out to be false, the world as adults knew it is suddenly turned upside-down, which causes stress. The things adults said in the presence of animals were actually understood by them when adults presumed they were not. This could cause anxiety, embarrassment, regret, and other "difficult to handle" emotions. Cruel words directed toward animals ("You're so ugly; "You're stupid") can't be taken back, which would be disturbing.
The new reality would require a period of adjustment wherein adults would have to deal with and overcome their emotions and any past transgressions toward animals while learning to communicate more effectively and appropriately with them.
Answer: If you're talking about in the past, he actually didn't do anything. Shane was going to tease/hurt Bernie with the stick, but Bernie grabbed it. Shane then lied to the zoo about Bernie attacking him which led to Bernie being moved. Although prior to Griffin kicking Shane's ass, Shane ended up cutting Bernie in the face.
Bishop73