The word “Muggots” in Cornwall meant intestines from a pig, and sometimes a calf. 
Here is an 1839 definition: “Muggety-Pie: a pie made of calf’s entrails. Cornwall.” 
Here is an 1882 definition: “Muggety-pie. A pie of sheep’s, sometimes calf’s entrails, flavoured with parsley, pepper, and salt, and enriched with cream.” 
Other writers have since noted that instead of using intestines from a sheep or calf, you could instead use those from a pig. Variations also suggest you can use lungs, liver and heart.
Cornish Recipes – Ancient and Modern gives 3 different recipes for it. One of the recipes calls for a few currants to be added to the meat mixture:
“Prepare a sheep’s pluck by soaking in water and thoroughly cleaning. Boil for several hours, and when cooked, put through mincing machine; then add a few currants, season well, and flavour with parsley or spice. Mix well together, put into a pie dish, cover with good short crust, and bake three-quarters hour.” 
The intestines are soaked first in water to get the smell out, then simmered for several hours, then minced. They are then seasoned with salt and pepper, perhaps also with parsley and an onion, then put in a pie dish, covered with pastry, and baked.
 Fred, W.P. Jago. The Ancient Language and the Dialect of Cornwall. Truro: Netherton & Worth. 1882.
 Grose, Francis and Samuel Pegge. A glossary of provincial and local words used in England. London: John Russell Smith. 1839.
 Martin, Edith. Cornish Recipes – Ancient and Modern. Truro: Cornwall Federation of Women’s Institutes, 1962 (originally published 1937.)