small pig
豘 centers on a small pig, specifically a piglet or young pig.
豘 combines 豕 (pig) with 屯, which likely contributes the sound. The exact historical development is uncertain.
The left side 豕 is a pig, and the right side 屯 looks like a sprout struggling to push through. Picture a tiny piglet, small and determined like a sprout, rooting around.
For トン, imagine a small pig weighing exactly one ton: ton -> トン, and the piglet is surprisingly heavy.