吞 is for swallowing whole, without chewing. 吞吞吐吐 (tūntūntǔtǔ) = to hesitate in speech (literally 'swallowing and spitting'), meaning to be evasive or mumbling.
memory
The character has 口 (mouth) at the top and 天 (heaven/sky) at the bottom — as if the mouth is swallowing the sky. Think big gulp.
