After a vigorous love making effort, the pubic region of ones body becomes wet, and the pubic hair gathers in wet tufts, or mattage.
Stella and Steve are very active love makers. The body fluids excreted during their love making is abundant. So much so that their entire masses of pubic hairs collect up the fluids and form peaks and knots. This is called mattage.
Lupin seed is used to enhance the verility of rams in agriculture. Apparently, it can increase the size of the testes up to four times. It is supposed that a gentleman with extremely well developed testes could be suspected of consuming lupin seed, or may just be called a lupin seed eater.
Jane was discussing her night with Jeremy to her sister, She commented on his genetalia stating that he must be eating lupin seeds. His testes were quite sizeable in nature, too big to be natural. Her sister commented, "Yeah, definitely a LUPIN SEED."