What's Been Suggested:
hot-glue handles on both bowls and pull. remove hot glue with denatured alcohol.
place in pillow case with edges facing away from you. spin around quickly to generate centrifugal force.
insert something between bowls (straw, paper, shim, icing spatula, automative feeler gauge blade, green onions, clear plastic reinforced with tape, thread, dental floss) then pull
professional-strength air compressor
similarly: tire/ball pump; canned air; syringe
strike the bowl as you would a bell, measure its frequency, suspend inner bowl by suction cup and string, excite the bowls' molecules at resonant frequency
tap bowls on various surfaces/ with various objects
application of vibration (electric toothbrush, top of washer/dryer, massage wand, sub-woofer, bladeless reciprocating saw)
drop repeatedly onto firm but soft surface
roll edge of outer bowl back and forth on towel-covered surface (preferably with a cat watching)
Heat It/ Cool It /Oil It/ Wet It/Dry It
boil upside-down in pot of water
fill with soapy water, seal with plastic wrap, invert, boil upside-down in microwave
various iterations of hot outside/cold inside; freezing/boiling/steaming
in the oven, put bowls upside down lifted up on a few ramekins, with a bowl of water underneath. heat oven to maximum temperature, leave for 1-2 hours or until inner bowl drops.
desiccate/evaporate bowls' interiors (submerge in rice, silica gel pack such as comes in many shoe boxes, and/or low heat)
various oil/lubricants suggested (butter, wd-40, bacon fat, silicone lube, dish soap; flour/talc/baby powder)
take bowls to higher elevation with lower atmospheric pressure
light candle, place bowls on top to create vacuum. may need to place on silicon mat or seal edges with wax.
call Auburn University's Foy Information Line at +1 (334) 844-4244
place where temperature/humidity vacilate, let nature do the work
find a vacuum chamber. place in there.
give to toddler with stern instructions not to separate.
Break one bowl.
Break both bowls.
Put on shelf out of sight and get new bowls.
Love is love. Respect their choice, let the bowls spoon.