However, upon entering the lens' beam, he finds himself returned to normal size and without danger of exploding. As the lens is covered with cave moisture, Palmer believes this has altered the beam to allow this strange effect. When subsequent experiments still result in objects exploding, Palmer concludes some unknown force in his own body allows him to safely size-shift.
However, when entering the lens' beam, he returns to normal size and no longer faces a risk of explosion. The lens being covered in cave moisture indicates it has altered the beam's properties, enabling this strange effect. Palmer deduces an unknown force within his body allows him to safely change sizes.