Back in the days when PANAM flew the Pacific skies and I was taxiing a 737 at Guam. ATC was a US Navy female who could rattle out a clearance so fast you just sat back and blinked.
The Pan American Airways 747 pilot requested the Airways Clearance and got a mouthful back starting with "Oakland ATC clears PANAM 47630 Heavy from Agana Airport to Honolulu via 15N 160 East at flight level 310, thence climb to flight level 330 . Be at flight level 330 by time ...etc...etc...etc Read back.
This was a lengthy clearance given at machine gun speed of transmission. Long silence ensued. Then from female ATC: PANAM 47630 Heavy - you copy?
Long silence - then from Panam in a slow Texas drawl: Say, Ma'am - could you maybe run that by me again, a little slower this time - I think I've just had a pen failure....