Reilly the Slug Gets His Comeuppance

Reilly was a slug, and I emphasise WAS, because he is no more. You see, he got his comeuppance.
My story begins long, long ago, a full three months previous.
“Morning, mum,” Reilly sang out, one wonderfully damp, drizzly cold morning.
“Good morning, Reilly,” his mother replied. “What has you so chirpy, apart from the fine day that is?”
“I don’t know,” her son replied. Mulling it over, he added, “Perhaps it’s because...”
“Because – what?” she asked, her head nudging a half-rotten cabbage leaf in his direction.
“You will think me silly...” he mumbled, eying the dainty morsel with some considerable delight.
“I will if you don’t eat your breakfast,” she chided, nudging the leaf closer to him.
Taking a bite out of the decaying leaf, Reilly said, “When I awoke this morning...”
“Yes?”
“I thought, I somehow knew – and I have absolutely no idea why – this is the day I leave home. Taking another mouthful of cabbage, he chomped away quite happily on it, then said, “Does this make any sense to you, mum?”
Smiling, tears of slime running freely down her slippery brown face, his mother said, “My child is all grown up!”