"But first, I conjecture that, although you all continue to look very interested and cheerful, you are in fact stressed out a lot by how I was asking you to do a task you were never previously taught how to do."

"But first, I conjecture that, although you all continue to look very interested and cheerful, even now that the task requiring that of you is over, you are in fact stressed out by how I was asking you to do something you were never taught how to do."

"But first, I conjecture that - although you all continue to look very interested and cheerful, even now that you're done with the task requiring you to control your expressions - you are in fact stressed out by how I was asking you to do something you were never taught how to do."

"But first, I conjecture that - although you all continue to look very interested and cheerful, even having finished the task requiring you to control your expressions - you are in fact stressed out by how I was asking you to do something you were never taught how to do."