it may not be your frogs tongue at all, possibly his stomach. Frogs sometimes will expel or throw up their stomachs as a means of getting rid of toxins as they cannot vomit the same as human beings do. My young pyxie frog had this issue after I fed it some bait store earthworms, it was quite disturbing to see before I had this knowledge. After I removed the substrate that was stuck to his exposed stomach with a q-tip and water, he swallowed his stomach and was ready for a meal. I have also read posts of ppl who said they fed their frogs as this was occuring and it helped by having them re-swallow their stomach as they simultaneously ate a cricket. Its a weird site but my frog appeared to be in no distress during the process. Hope this helps.