He is probably rattling his tail while feeding because you are looking at him and he is saying "STAY AWAY, I am Big and Mean and poisonous" as he is busy with swollowing and because of that, more volunerable (and hence, more nervious). Once my corns take their meal and constrict it, I leave them alone for a good 20-30mins, only peaking in to ensure they did eat their food, instead of killing (or going through the motions, as I feed nearly exclusively fresh killed or frozen thawed). A few times I had snakes grab, constrict and then fail to eat the food, either because it was too big or it just didn't want to....only to realize a few days later, when I kept noticing a very foul stench....trust me, better to avoid that at all costs LOL. Hence now I take a quick peak after 30 minutes to a few hours...(sometimes I forget or get distracted and forget to check sooner LOL) to make sure no sign of the prey is still in the cage.