mouth problem

[tigger]

i have a friend whoes little guy is now 6 months old and has been fine until yesterday. he is a vield and has been eating but this morning she said he tried to eat and could only open his mouth a bit and his tounge is turning black and he wouldn't uncurl it so he went to the food dish and chomped 2 crickets.
any ideas of what this might be and what should she do
thanks
glen