My experience was that boisterous shenanigans, like juggling testicles or something, would absolutely not have been tolerated. Indeed, the mood was somber/business-like enough that no one even dared.

On the other hand, a whispered inoffensive remark to your lab partner would be okay. Something this like this would probably be okay:

-- "Be careful not to knick the nerve as you <whatever>"

-- "Opps! Better now?

-- "Yes. In fairness, it's not her biggest problem right now"