Complex sentence: The major symptoms will be developed just a few hours of toxin ingestion: vomiting, diarrhea, numbness of extremities, mouth and lips, reversal of hot and cold sensation, muscle and joint aches.
Split into simpler sentences: The major symptoms will be developed just a few hours of toxin ingestion. There are: vomitting, diarrhea, numbness of extremities, mouth and lips, reversal of hot and cold sensation, muscle and joint aches.