Approach: Continental xxx, slow to one hundred and ninety.

Continental (in a slow Texas drawl): Roger, slowing one-nine-zero.

After a few minutes of handling other arrivals, Approach asked Continental to slow further to 160.

Again the drawling pilot acknowledged the speed reduction.

Sereral more minutes passed and the controller still needed more spacing.

Approach: Continental xxx, slow to one hundred and fifty.

Continental: (in an even slower, more exasperated voice): Do you guys know what the stall speed of a seven-five-seven is ?

Approach (without missing a beat): No sir, but if you ask the guy in the left seat, I'm sure he could tell you.

Delta xxx descend and maintain six-thousand........ Nothing further was heard from the Continental crew.