Question for those who have attended a sitcom taping or have worked on a sitcom?

This may be a little hard to explain, but here goes. Sometimes when I watch a show something funny happens, but it isn't funny until something is revealed to the home viewer, but for some reason the studio audience doesn't laugh until the revelation is made either. Why is that?

For example, (this is just a general example, not anything from a specific show) let's say a guy is talking to someone who is at his side, but off screen and so can't be seen by people watching at home. What the person is saying to this unseen individual might not be funny, until the next shot reveals to the home viewer that he's talking to a chimpanzee wearing a funny hat, and then the studio audience bursts into laughter.

Why is it that the studio audience doesn't laugh until the chimp is shown to the at home viewer? Can't they see him the whole time, or is he somehow hidden from view and then revealed to the studio audience as well?

Cuz there is a sign that lights up that tells them to laugh and clap when the producers want you to laugh. But if you hear just laughter its cuz the sign is off but there is a HYPE man or woman signaling the audience to just laugh but not clap or scream...

because there is a light up sign that tells them when to clap laph and thing like that

I think that someone tells them when to laugh or like you said see what you see at home (they don't sse the chimpanzee)