system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: When a judge strikes something from the record and instructs the jury to forget that portion of what was said in a trial, how does he make sure they do not use that information later when they deliberate?
gpt
You literally cannot, save for occasions where one juror rats out another. This is why good judges try very carefully to guide the lawyers and witnesses to avoid any fatal missteps. If somebody says something that's sufficiently improper or inadmissible, it can result in a mistrial or a verdict that's overturned on appeal. The courts recognize exactly what you have: that some things simply can't be cured with an instruction. 

And to be clear, judges don't tell the jury to "forget" the testimony, again recognizing that humans can't do that. The judge will normally instruct the jury to wall it off in their mind, and to remind themselves that they can't consider the stricken testimony.