But what if the card has no room for flavor text? Well, then you have to read magicthegathering.com.
We turn now to the case of Quicksilver Behemoth. Its affinity for artifacts ability combined with its Phanton Whelp-like drawback fill up its text box, leaving no room for explanatory flavor text. So why is this 4/5 Beast constantly bouncing back to its owner's hand? And why, in the art, does it look like it just swallowed a Fire Elemental?
Let's take a behind-the-scenes look at the card's art description to find out.
A water elemental charged with electricity. It dissipates on impact with an enemy creature, dousing and electrocuting it. (Creature type could change to beast.)
Now we see the explanation. The Behemoth is a nimble underwater predator with the natural weaponry of electricity, like an electric eel. This explains the mechanic: when the Behemoth engages in combat with an enemy (when it attacks or blocks), it discharges (deals combat damage) and then scoots away (returns to its owner's hand). It also explains the art: the glow around its throat is the artist's (Anthony S. Waters's) rendition of its electric ability, demonstrating how it deals that damage (well, the electricity plus those teeth and nasty hooked claws).
Now you know.