They're about to step on him and smother him so he knows how much of an effect he has had on their growth.

Mangle and Rin teasing Len with their scent that is too addicting.. He takes a whiff and as a reaction they start to expand and grow. (1 more pic in replies)

Even though I’m not gonna post much and just retweet stuff. I think it was time to have an account here! Hewwo!